From the experiments described by the author in a former paper, it appeared that a magnetized needle vibrated under exposure to the sun’s rays, came to rest sooner than when screened from their influence; that a similar effect was produced on a needle of glass or of copper, but that the effect on the magnetized needle greatly exceeded that upon either of the others. In the prosecution of this inquiry, the author has endeavoured to vary the experiments so as to obviate several causes of inaccuracy which might tend to invalidate the general conclusions he had before drawn. His first object was to compare the effects of the solar rays on an unmagnetized steel needle with one that was magnetized under the same circumstances; and the result was, that the latter was influenced in a more considerable degree than the former; and a similar difference was observed when the vibrations of a magnetized needle were compared with those of a needle made of glass or of copper. He ascertained that the diminution of the terminal arc of vibration, on exposure to the sun, was not occasioned merely by the heat imparted to the needles or surrounding medium, although this cause appeared in some instances to measure the intensity of the action which produced the diminution. In order to determine the comparative influence of the separate rays, he allowed them to fall on the needles after transmission through differently coloured fluids and glasses; but owing to want of opportunity, he was obliged to abandon the inquiry before arriving at any determinate results: though as far as they went, they appeared to confirm the conclusion that the effects were dependent on the degree of light, and not on that of the heat. The red rays, however, appeared to have a greater effect in diminishing the terminal arc than the blue. In order to determine the single effect of temperature, independently of light, the needles were vibrated in close vessels surrounded with water of different temperatures; the results showed that the terminal arc was increased in air of higher temperatures, which is the reverse of what takes place from the direct influence of the solar rays; and that this effect, instead of being different in the magnetized and in the other needles, was nearly the same in all, of whatever materials they consisted, and whether magnetized or not. The author next endeavoured to ascertain the effects produced on the axes of vibration by the action of a common fire; these, though much less in degree, he found to be similar in kind to those of the sun.
The effect of temperature, salinity and nitrogen products on food consumption of pink shrimp Farfantepenaeus paulensis
