434 SCIENTIFIC RECORD FOR 1884. 



The fraction of the total energy which can be converted into work, ac- 

 cording to the second law, depends on the difference of the initial and 

 final temperatures. In optics, Cornu's ingenious application of Dop- 

 pler's principle to determine whether a spectrum line is solar or terres- 

 trial in origin is mentioned. An image of the sun is thrown on the 

 slit of the spectroscope and caused to vibrate two or three times a sec- 

 ond, so that the light entering the instrument comes alternately from 

 the advancing and the retreating edge. Since the line, if solar, suffers 

 in this way alternate displacements, it appears to tremble,, while if ter- 

 restrial it appears fixed. In acoustics the curious fact is stated that 

 while when a pure note, such as that of a tuning-fork, is sounded, we 

 cannot tell whether the sound comes to us from in front or from behind, 

 when any other sort of sound is produced, from a clap of the hand to 

 the clearest vowel sound, the discrimination is not only possible but 

 easy and instinctive. The address concludes with a discussion of the 

 importance of experimental science in a system of education. {Natitre, 

 August, 1884, XXX, 410-417.) 



As president of the mathematical and physical section, Sir William 

 Thomson gave an address entitled " Steps toward a kinetic theory of 

 matter," in which, after giving a resume of the kinetic theory of gases, 

 and discussing especially the theory of the repulsive action between 

 molecules in collision, he takes up the question of elasticity and shows 

 that any ideal system of material particles acting on ooe another mu- 

 tually through massless connecting springs, may be perfectly imitated 

 in a model consisting of rigid links jointed together, and having rapidly 

 rotating fly-wheels pivoted on some or on all of the links. He figures 

 two systems, each consisting of two hooked rods, connected in the first 

 to an elliptical spring, and in the second to the opposite corners of a 

 square frame loosely articulated, upon each of the sides of which, as 

 an axis, is a fly-wheel or gyrostat in rapid rotation. If either of these 

 systems be hung up by the hook on one of its projecting rods, and a 

 weight be placed on the hook on the other rod, the weight when first 

 put on will oscillate up and down, and will go on doing so forever if the 

 system be absolutely unfrictional. Thus, out of matter jjossessing ri- 

 gidity, but absolutely devoid of elasticity, a perfect model of a spring 

 has been made in the form of a spring- balance. {Xature, August, 1884, 

 XXX, 417-421.) 



The second and third volumes of the " Travaux et M^moires " of the 

 Bureau International des Poids et Mesures have been published during 

 1883 and 1884, the first volume having appeared in 1881. The second 

 volume contains papers by Dr. Benoit on his expansion experiments, 

 by M. Marek on the methods and results of the weighings made at the 

 bureau from 1879 to 1881, and by Dr. Broch, the director, on the ex- 

 pansion of mercury. The third volume contains an account of the modes 

 of comparison of the standards, with descriptions of the ai)paratus used 

 and a complete statement of the observations and the methods pf their 



