The Crucial Experiments

2016 ◽  
pp. 117-145
Keyword(s):  
Author(s):  
André Parent

Two hundred years ago, Giovanni Aldini published a highly influential book that reported experiments in which the principles of Luigi Galvani (animal electricity) and Alessandro Volta (bimetallic electricity) were used together for the first time. Aldini was born in Bologna in 1762 and graduated in physics at the University of his native town in 1782. As nephew and assistant of Galvani, he actively participated in a series of crucial experiments with frog's muscles that led to the idea that electricity was the long-sought vital force coursing from brain to muscles. Aldini became professor of experimental physics at the University of Bologna in 1798. He traveled extensively throughout Europe, spending much time defending the concept of his discreet uncle against the incessant attacks of Volta, who did not believe in animal electricity. Aldini used Volta's bimetallic pile to apply electric current to dismembered bodies of animals and humans; these spectacular galvanic reanimation experiments made a strong and enduring impression on his contemporaries. Aldini also treated patients with personality disorders and reported complete rehabilitation following transcranial administration of electric current. Aldini's work laid the ground for the development of various forms of electrotherapy that were heavily used later in the 19th century. Even today, deep brain stimulation, a procedure currently employed to relieve patients with motor or behavioral disorders, owes much to Aldini and galvanism. In recognition of his merits, Aldini was made a knight of the Iron Crown and a councillor of state at Milan, where he died in 1834.


Author(s):  
Víctor Manuel Hernández

Although Pierre Duhem is well known for his conventionalist outlook and, in particular, for his critique of crucial experiments outlined in his thesis on the empirical indeterminacy of theory, he also contributed to the scholarship on the psychological profiles of scientists by revising Pascal’s famous distinction between the subtle mind and the geometric mind (esprits fins and esprits géométriques). For Duhem, the ideal scientist is the one who combines the defining qualities of both types of intellect. As a physicist, Duhem made important theoretical contributions to the field of thermodynamics as well as to the then-nascent physical chemistry. Due to his rejection of atomism and his unrelenting critique of Maxwell’s electrodynamics, however, in his later years, Duhem’s work was surpassed and abandoned by the dominant tendencies of physics of the time. In this essay, I will discuss whether Duhem himself can be understood through the lens of his own account of the scientist’s psychological profile. More specifically, I examine whether the subtle mind – to which he seems to assign greater cognitive value – in fact plays a key role in Duhem’s critique of the English School (école anglaise), or if his preference for the axiomatic structure of theoretical physics shows a greater affinity with the geometric mind.


1974 ◽  
Vol 36 (6) ◽  
pp. 334-348 ◽  
Author(s):  
Anton E. Lawson
Keyword(s):  

1998 ◽  
Vol 15 (1) ◽  
pp. 19-23
Author(s):  
Andrea Ferrara

AbstractI review the capabilities of Hα observations to constrain some aspects of the current models of the interstellar medium. In particular, it is shown that turbulence is a necessary ingredient of any viable model, since most of the energy produced by supernova explosions and ionising radiation is stored in kinetic form in the ISM. Various forms of turbulent energy dissipation, including cloud collisions, are analysed. Two additional aspects, concerning the existence of galactic fountains and their relation with high-velocity Clouds, and the extended ionised layer of spiral galaxies are discussed; some crucial experiments are suggested.


Experiments are described in which the phenomenon of wave-interaction (‘Luxembourg effect’) is used to provide information about the height at which radio waves of different frequencies are absorbed in the ionosphere. It is first, demonstrated by two crucial experiments that the absorption mechanism suggested by Bailey & Martyn (1934 a and b ) is the true one. Measurements of the phase of the modulation transferred from one wave to the other by the non-linear absorption process in the ionosphere are described; and it is shown how, by measuring this phase at different modulation frequencies, it is possible to locate the region where the interaction occurs. The results of a series of experiments summarized in tables 2, 3 a and 3 b and figures 8 and 9 are discussed. The conclusion is reached that the frequency with which electrons collide with neutral molecules at a height of about 85 km. is of the order 5 x 10 5 sec. -1 , and that this is the height near which the main absorption of waves of frequency 1 Mcyc./sec. and 200 kcyc./sec. are absorbed at night. Waves of frequency 90 and 68 kcyc./sec. are absorbed, and possibly also reflected, below this level. With the approach of dawn the regions responsible for absorbing 1 Mcyc./sec. and 200 kcyc./sec. waves drift apart. The theory of Bailey & Martyn (1934 b ) and Bailey (1937 a ) is related to modern theories of ionospheric absorption and is restated with the standard nomenclature of Appleton’s magneto-ionic theory.


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