scholarly journals II. On the spectra of some of the fixed stars

1864 ◽  
Vol 13 ◽  
pp. 242-244 ◽  
Keyword(s):  
Focal Length ◽  
Cylindrical Lens ◽  
Narrow Line ◽  
Stellar Spectra ◽  
Flint Glass ◽  
Small Telescope ◽  
Dispersive Power ◽  
Different Parts ◽  
General Method ◽  
Collimating Lens

After a few introductory remarks, the authors describe the apparatu which they employ, and their general method of observing the spectra the fixed stars and planets. The spectroscope contrived for these inqu ries was attached to the eye end of a refracting telescope of 10 feet foe length, with an 8-incli achromatic object-glass, the whole mounted equa torially and carried by a clock-movement. In the construction of th spectroscope, a plano-convex cylindrical lens, of 14 inches focal length, wa employed to convert the image of the star into a narrow line of light which was made to fall upon a very fine slit, behind which was placed an achromatic collimating lens. The dispersing portion of the arrangement consisted of two dense flint-glass prisms; and the spectrum was viewe through a small achromatic telescope with a magnifying power of between 5 and 6 diameters. Angular measures of the different parts of the spectrum were obtained by means of a micrometric screw, by which the position of the small telescope was regulated. A reflecting prism was placed over one half of the slit of the spectroscope, and by means of a mirror, suitably adjusted, the spectra of comparison were viewed simultaneously with the stellar spectra. This light was usually obtained from the in­duction spark taken between electrodes of different metals. The dispersive power of the apparatus was sufficient to enable the observer to see the line Ni of Kirchhoff between the two solar lines D ; and the three constituents of the magnesium group at b are divided still more evidently*. Minute details of the methods adopted for testing the exact coincidence of the corresponding metallic lines with those of the solar and lunar spectrum, are given, and the authors then proceed to give the results of their obser­vations.

scholarly journals An account of a series of experiments made with a view to the construction of an achromatic telescope with a fluid concave lens, in stead of the usual lens of flint glass. In a letter addressed to Davies Gilbert, Esq. M. P. President of the Royal Society. By Peter Barlow, Esq. F. R. S. &c

1833 ◽  
Vol 2 ◽  
pp. 333-334
Keyword(s):  
Focal Length ◽  
Flint Glass ◽  
Double Ring ◽  
Proper Distance ◽  
Concave Lens ◽  
Satellites Of Jupiter ◽  
Series Of Experiments ◽  
Focal Power ◽  
Dispersive Power ◽  
William Herschel

The idea of constructing achromatic telescopes with fluid lenses was first suggested to the author by the attempt of Messrs. Gilbert to apply to practice the principles and rules for the construction of aplanatic object-glasses, laid down by Mr. Herschel in the Philosophical Transactions for 1821. In following these suggestions, the author became sensible of the difficulty of obtaining flint glass of sufficient size and purity for astronomical telescopes; and was thence led to consider the possibility of substituting some fluid in place of flint glass. Dr. Blair had, many years ago, succeeded in making very perfect telescopes of this description, but he still retained the use of flint glass. Among the various fluids adapted to this optical purpose, the author gave a decided preference to the sulphuret of carbon, which combines properties of perfect transparency and freedom from colour, with a refractive index nearly equal to that of flint glass, and with a dispersive power more than double, properties which it appears to retain under all the temperatures to which it is likely to be exposed in an astronomical telescope. After several trials, Mr. Barlow determined the best method of confining this fluid, but was at first unsuccessful in his attempts to construct with it a telescope of 6 inches aperture and 7 feet in length. He afterwards undertook a smaller one of 3 inches aperture, which he at length accomplished, and in the very first trials with it was able to separate a great number of double stars of the class which Sir William Herschel has pointed out as tests of a good 3½-inch refractor. Encouraged by his success, he again attempted a 6-inch object-glass, with a different manner of adjusting and securing the lenses, and considers the result of his endeavour as proving at least the practicability of the construction. This instrument, with a power of 143, shows the small star in Polaris so distinct and brilliant, that its transit might be taken with the utmost certainty; it exhibits distinctly the small stars in α Lyræ, Aldebaran, Rigel, &c. and decidedly separates Castor, γ Leonis, and ϵ Bootis. The belts and double ring of Saturn are well exhibited with a power of 150; and the belts and satellites of Jupiter are tolerably defined with the same power, but will not bear a higher power than about 200. In the usual construction of achromatic telescopes, the two or the three lenses composing the object-glass are brought into immediate contact. But the high dispersive power of the sulphuret of carbon enables Mr. Barlow to place the fluid correcting lens at a distance from the plate object lens equal to half its focal length. By this means the fluid lens, which is the most difficult part of the construction, is reduced to one half or less of the size of the plate lens. This construction, therefore, renders us independent of flint glass, enables us to increase the aperture of the telescope to a considerable extent; and gives us all the light, field, and focal power of a telescope of one and a half time the length of the tube. The author investigates analytically the formulæ for calculating the proper distance of the lenses on this construction, and expresses a hope that further experiments will enable us to determine the precise distance which shall reduce what has been termed the secondary spectrum, inseparable from the ordinary construction, either to zero, or to an inconsiderable amount.

scholarly journals Experiments relative to the effect of temperature on the refractive index and dispersive power of expansible fluids, and on the influence of these changes in a telescope with a fluid lens

1833 ◽  
Vol 2 ◽  
pp. 345-346
Keyword(s):  
Refractive Index ◽  
Focal Length ◽  
Effect Of Temperature ◽  
Focal Power ◽  
Dispersive Power

In a paper lately read to the Society, the author stated that he had not perceived any change in the focal length of the telescope, induced by changes of temperature; but he has since ascertained that in order to produce the brightest and most perfect image, the distance of the object-glass requires a minute adjustment, amounting to 0·134 of an inch, corresponding to an elevation of temperature from 57° to 84°, or a depression from 57° to 31°. In order to introduce greater clearness and precision, the author proceeds to define certain terms which he finds it necessary to employ. By the length of the telescope , he would be understood to mean the distance between the object-glass and the focus; by the fluid focus , that between the fluid lens and the focus; and by the focal power of the telescope, he means the focal length of a telescope of the usual construction, which gives the same convergency to the rays, or produces an image of the same size: but he also employs the term focal length of the telescope , as synonymous with the first; that of fluid focal length as synonymous with the second; and that of equivalent focal length as synonymous with the last of these terms.

scholarly journals II. On the spectra of some of the chemical elements

1864 ◽  
Vol 154 ◽  
pp. 139-160 ◽  
Keyword(s):  
Chemical Elements ◽  
Solar Spectrum ◽  
Standard Scale ◽  
The Difference ◽  
Dispersive Power ◽  
Different Parts

1. I have been engaged for some time, in association with Professor W. A. Miller, in observing the spectra of the fixed stars. For the purpose of accurately determining the position of the stellar lines, and their possible coincidence with some of the bright lines of the terrestrial elements, I constructed an apparatus in which the spectrum of a star can be observed directly with any desired spectrum. To carry out this comparison, we found no maps of the spectra of the chemical elements that were conveniently available. The minutely detailed and most accurate maps and tables of Kirchhoff were confined to a portion of the spectrum, and to some only of the elementary bodies; and in the maps of both the first and the second part of his investigations, the elements which are described are not all given with equal completeness in different parts of the spectrum. But these maps were the less available for our purpose because, since the bright lines of the metals are laid down relatively to the dark lines of the solar spectrum, there is some uncertainty in determining their position at night, and also in circumstances when the solar spectrum cannot be conveniently compared simultaneously with them. Moreover, in consequence of the difference in the dispersive power of prisms, and the uncertainty of their being placed exactly at the same angle relatively to the incident rays, tables of numbers obtained with one instrument are not alone sufficient to determine lines from their position with any other instrument. It appeared to me that a standard scale of comparison such as was required, and which, unlike the solar spectrum, would be always at hand, is to be found in the lines of the spectrum of common air. Since in this spectrum about a hundred lines are visible in the interval between a and H, they are sufficiently numerous to become the fiducial points of a standard scale to which the bright lines of the elements can be referred. The air-spectrum has also the great advantage of being visible, together with the spectra of the bodies under observation, without any increased complication of apparatus.

scholarly journals On the action of the rays of the spectrum on vegetable juices: being an extract from a letter by Mrs. M. Somerville to Sir John F. W. Herschel, Bart., dated Rome, September 20, 1845. Communicated by Sir John F. W. Herschel, Bart., F. R. S

1851 ◽  
Vol 5 ◽  
pp. 569-570 ◽  
Keyword(s):  
Solar Spectrum ◽  
Maximum Intensity ◽  
Flint Glass ◽  
Different Parts

In the experiments of which the results are here recorded, the solar spectrum was condensed by a lens of flint glass of seven inches and a half focus, maintained in the same part of the screen by keeping a pin-hole or pencil-mark constantly at the corner of the red rays, which were sharply defined by being viewed through blue spectacles; and the apparatus was covered with black cloth in order to exclude extraneous light. Thick white letter-paper, moistened with the liquid to be examined, was exposed wet to the spectrum, as it was found that the action of the coloured light was thus rendered more immediate and more intense, than when the surface of the paper was dry. The action of the spectrum at the junction of the lavender with the violet rays was found in some cases to be different from what it is with either of these colours separately, indicating a break in the continuity of action, and suggesting the idea of a secondary spectrum. In many instances the yellow and green rays exert a powerful influence on vegetable substances, an influence apparently unconnected with heat; for the darkening is generally least under the red rays and immediately below them, where the calorific rays are most abundant. The action, in a great number of cases, produces insulated spots in different parts of the spectrum, but more especially in the region of the rays of mean refrangibility, in which neither the calorific nor the chemical powers are the greatest. The point of maximum intensity is sometimes altered by the addition of acids, alkalies, or diluted alcohol. But altogether, as the author states, the action of the different parts of the spectrum seems to be very capricious, the changes of colour produced being exceedingly irregular and unaccountable.

Positional accuracy of boundaries between clearcuts and mature forest stands delineated by means of aerial photointerpretation

1998 ◽  
Vol 28 (3) ◽  
pp. 368-374 ◽  
Author(s):  
Erik Næsset
Keyword(s):  
Focal Length ◽  
Ground Truth ◽  
Aerial Photographs ◽  
Forest Stands ◽  
Positional Accuracy ◽  
Black And White ◽  
Mature Forest ◽  
Film Type ◽  
Mature Stands ◽  
Different Parts

Four skilled interpreters delineated 48 boundaries between mature forest stands and clear-felled or nonproductive areas using black and white and color infrared aerial photographs. The positions of the boundaries were compared with ground-truth points located along the boundaries. On average, the interpreters located the boundaries 1.22-2.44 m inside the mature forest stands. Film type, focal length, location of the boundaries within different parts of the stereo models, and the height of the trees along the boundaries did not affect the interpretations significantly. Shadows caused by the trees, which is a hinderance to ground visibility, seriously affected the interpretation. The interpreters placed the boundaries 0.62 m farther inside the mature stands for boundaries covered by shadow than for boundaries without shadows.

scholarly journals Two-dimensional laser-induced incandescence for soot volume fraction measurements: issues in quantification due to laser beam focusing

2020 ◽  
Vol 126 (12) ◽  
Author(s):  
Manu Mannazhi ◽  
Per-Erik Bengtsson
Keyword(s):  
Laser Fluence ◽  
Volume Fraction ◽  
Focal Length ◽  
Laser Sheet ◽  
Soot Volume Fraction ◽  
Cylindrical Lens ◽  
Two Dimensional ◽  
Beam Focusing ◽  
Wide Range ◽  
Laser Induced Incandescence

AbstractTwo-dimensional laser-induced incandescence (LII) measurements usually involve the use of a cylindrical lens to illuminate the planar region of interest. This creates a varying laser fluence and sheet width in the imaged flame region which could lead to large uncertainties in the quantification of the 2D LII signals into soot volume fraction distributions. To investigate these effects, 2D LII measurements using a wide range of laser pulse energies were performed on a premixed flat ethylene–air flame while employing a cylindrical lens to focus the laser sheet. Using shorter focal length of the focusing lens resulted in larger variation of the LII signal profiles across the flame. A heat – and – mass – transfer - based LII model was also used to simulate the measurements and good agreement was found. The ratio between focal length (FL) and image length (IL) was introduced as a useful parameter for estimating the bias in estimated soot volume fractions across the flame. The general recommendation is to maximize this FL/IL ratio in an experiment, which in practice means the use of a long focal length lens. Furthermore, the best choices of laser fluence and detection gate width are discussed based on results from these simulations.

Anatomy of the Regional Differences in the Eye of the Mantis Ciulfina

1979 ◽  
Vol 80 (1) ◽  
pp. 165-190 ◽  
Author(s):  
G. A. HORRIDGE ◽  
PETER DUELLI
Keyword(s):  
Regional Differences ◽  
Compound Eye ◽  
Focal Length ◽  
Visual Fields ◽  
Resolving Power ◽  
Acceptance Angle ◽  
Extended Source ◽  
Angular Coordinates ◽  
The Individual ◽  
Different Parts

In the compound eye of Ciulfina (Mantidae) there are large regional differences in interommatidial angle as measured optically from the pseudopupil. Notably there is an acute zone which looks backwards as well as one looking forwards. There are correlated regional differences in the dimensions of the ommatidia. The following anatomical features which influence the optical performance have been measured in different parts of the eye The facet diameter is greater where the interommatidial angle is smaller. This could influence resolving power, but calculation shows that facet size does not exert a dominant effect on the visual fields of the receptors. The rhabdom tip diameter, which theoretically has a strong influence on the size of visual fields, is narrower in eye regions where the interommatidial angle is smaller. The cone length, from which the focal length can be estimated, is greater where the interommatidial angle is smaller. Estimation of the amount of light reaching the rhabdom suggests that different parts of the eye have similar sensitivity to a point source of light, but differ by a factor of at least 10 in sensitivity to an extended source. There is anatomical evidence that in the acute zone the sensitivity has been sacrificed for the sake of resolution. Maps of the theoretical minimum fields of the photoreceptors, plotted in their positions on the eye in angular coordinates, suggest that there are too few ommatidia for the eye as a whole to reconstruct all the visual detail that the individual receptors can resolve. The conclusion from (3) and (4), together with some behavioural evidence, suggests that the eye structure must make possible the resolution of small movements of contrasting edges and of small dark contrasting objects but there is less emphasis on the total reconstruction of fine patterns because the interommatidial angle is greater than the estimate of the acceptance angle.

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