712 



PHYSICS, PROGRESS OF, IN 1890. 



of the wave length of yellow light. Van der 

 Mensbrugghe concludes, from experiments on 

 liquids, especially from the modification of cap- 

 illary phenomena by local heating and by dis- 

 solved substances, . that Gauss's theory agrees 

 with the facts, while those of Laplace and Pois- 

 son do not. Prof. C. Michie (Edinburgh Royal 

 Society, March 17) has observed surface tension 

 by means of the ripples started by a tuning 

 fork. These were photographed, and the nega- 

 tives were measured micrometrically. He was 

 thus able to measure the surface tension of mer- 

 cury, and to prove that it is reduced more than 

 20 per cent, by strong electrification. 



Expansion and Compression. Prof. A. M. 

 Worthington (London Physical Society, June 

 20) has measured the extension of a liquid col- 

 umn by three methods that of the barometer 

 tube, the centrifugal method, and that of slow 

 cooling. He thus submitted water to an exten- 

 sive force of 7'9 atmospheres, sulphuric acid to 

 12, and alcohol to 17. The coefficient of extensi- 

 bility in all cases was much less than that of com- 

 pressibility. The results are astonishing when 

 it is considered that liquids are usually thought 

 to have no extensibility at all. A. E. Tutton 

 (" Nature.'' Oct. 16) has found that many lique- 

 fied gases expand enormously when heated, as 

 compared with ordinary liquids, the expansion 

 sometimes exceeding that of the unliquefied gas. 

 Thus, the coefficient of expansion of liquid chlo- 

 rine at 86 is -00346 nearly that of gaseous 

 chlorine, and before the critical temperature 

 of 146 is reached the coefficient is considerably 

 higher than that of the gas. Prof. P. G. Tait, in 

 the report on the physics of the " Challenger " 

 expedition, describes elaborate experiments on 

 the compressibility of water. The average com- 

 pression of fresh water at C., and at low pressure, 

 is 520 x 10~ 7 per atmosphere, with the minimum 

 at 66. The compressibility and the temperature 

 of the minimum are both lowered by increased 

 pressure. At 456*9 atmospheres the average 

 compression is 478 x 10~ 7 per atmosphere, and 

 the temperature of minimum compressibility is 

 about 30 C. The average compression of sea 

 water is '92 that of fresh, and the minimum is 

 56 at atmospheric pressure. The depth of a sea 

 six miles deep is reduced 620 feet by the com- 

 pression due to its own weight. The general 

 level of the ocean is reduced 116 feet by such 

 compression, and if the compressibility of water, 

 infinitesimal as it is, should vanish* 2,000,000 

 square miles of land would be submerged. Prof. 

 S. U. Pickering (' Philosophical Magazine," No- 

 vember) has examined the curves that represent 

 the varying density of water at different tem- 

 peratures, and finds that there are changes of 

 curvature at 18 and 10. He thinks that a 

 liquid is composed of various partially dissociated 

 aggregates of their fundamental molecules ; and 

 such complicated bodies would necessarily be un- 

 stable. Other liquids, such as ethyl chloride, 

 methyl bromide, carbon disulphide, and the alco- 

 hols, show similar changes. 



Water Drops. C. V. Boys (London Physical 

 Society, May 2) has succeeded, by exposures of 

 5^-ff second about twenty times a second, in pho- 

 tographing water drops, showing their forma- 

 tion, their breaking away, their oscillation, and 

 their rebound from the liquid surface they 



strike. The zootrope reproduces the phenomena 

 in a very striking manner. 



Barometry. The largest water barometer ever 

 made has been placed in St. Jacques's Tower, 

 Paris. It is 12-69 metres long and 2 centimetres 

 in diameter. It has a special registering appara- 

 tus, and is said to be very active during thun- 

 der storms. 



Sound. Velocity of Propagation. Gen. A. 

 W. Greely gives the following measurements at 

 very low temperatures : 



The diminution of velocity with the tempera- 

 ture was 0-603 metre per degree. Violle and 

 Vautier (Paris Academy of Sciences, Feb. 3) 

 show that in a cylindrical tube, whatever the 

 impulse, a sound wave tends toward a simple 

 determined form, and that when this is once ac- 

 quired, the various parts of the wave are propa- 

 gated with normal velocity. In the open air 

 this is greater than in a tube, where the wave is 

 retarded in inverse ratio to the diameter. 



Bells. Lord Rayleigh (" Philosophical Maga- 

 zine," January) has experimented on the tones of 

 bells, chiefly with the object of finding the dif- 

 ference between the good and the bad, with re- 

 spect to the perfect harmony of the various notes 

 each gives. The task of making a perfectly con- 

 sonant bell is not hopeless, he thinks: but so 

 much tentative work would be required that it is 

 not likely soon to be accomplished. Haweis 

 (1878) says that a "true" Belgian bell gives its 

 dominant note if struck a little above the rim. 

 the third when struck two thirds up, and the 

 fifth near the top ; and that a true bell is that in 

 which the third and fifth are heard in right rela- 

 tive subordination to the fundamental. Rayleigh 

 says that many more tones than these usually 

 occur. Five of the bells that he tested gave the 

 following : 



pi 



a -,-6 

 d'~3 



a+8 



ff'tt- 



a' + 6 

 c"Jt+4 



d'-6 

 a'tf-5 



d" + 8 



ff'ttt 10 

 b" + 2 



The figures after the notes indicate the num- 

 ber of vibrations by which they were out of 

 tune. 



Thermopnone. Kallemann. in a recent inaugu- 

 ral at Halle, describes experiments on what he 

 calls a drahtthermophon. This consists of a 

 source of sound, a microphone, battery, and 

 stretched wire, one end of which is fastened to a 

 membrane connected with a resonator. 



With a variable current the wire lengthened 

 and shortened rapidly, setting the membrane in 

 vibration. The strength of current, the tension 

 of the wire, and its thickness all influenced 

 the strength of the sound ; but the length of the 

 wire had nothing to do with it, a sound being 

 obtained with a wire one centimetre long. The 

 direction of current also was without influence, 

 which points to a thermal origin of the sound. 



Timbre. Prof. Rudolf Koenig has made ex- 

 periments which extend Helmholtz's classical re- 



