SCIENCE. 



227 



Mean oj the above series. 





+ 



1.44 



100 



2.00 



1. 01 



J-45 



1. 00 



1. 71 



1.07 



1.67 



1. 19 



1.50 



1.00 



2.00 



1. 01 



Means, 1.68 



1.04 



1.68 — 



1.04 



Per cent. 



1.68 



Thus with the apparatus working most perfectly, the 

 analyzer succeeded in extinguishing or quenching 38 per 

 cent, of the polarized wave, a percentage too great to be 

 mistaken. Considering the analyzer and polarizer as 

 equally efficient, the real percentage of polarization by 

 polarizer would be 62 per cent., and of the analyzer 62 

 per cent., as is evident frcm the fact that 62 per cent, of 

 62 per cent, is 38 per cent. Thus, cither part of the 

 apparatus obliterates over half of the wave attempting 

 transmission, a fraction which would be unmistakably 

 visible in polarized light. 



These results establish the following facts for sound 

 waves or for undulations, viz.: 



1st. A decided reflection occurs at a surface separating 

 two gases of different density, confirming the views of 

 Henry and Tyndall in this regard. 



2d. In repeated reflection from such surfaces the inten- 

 sity of the final component varies with the relative posi- 

 tions of those surfaces, the same following the laws of 

 polarization in light, from which we conclude that longi- 

 tudinal undulations can be polarized. 



With sound polarized, we complete the list of effects 

 for longitudinal undulations which are known to light , 

 viz.: radiation, shadows, reflection, refraction, diffusion, 

 diffraction, interference and polarization ; for the laws are 

 common for like conditions, viz.: for intensity of radiation 



in ambient space, -— ; in paral.el space, ; in prismatic 



space, like a tube, 



for shadows, reflection, refrac- 



tion and interference as well known ; for diffusion, as 

 when a steam whistle is sounded, filling the air with its 

 resounding ring ; for diffraction, ss sound waves diverg- 

 ing rapidly after passing a narrow space between build- 

 ings, like light in passing a narrow slit and diverging ; 

 and, finally, for polarization, as above. In studying these 

 comparisons we should recollect the vast difference be- 

 tween the properties of undulations in heavy, and 

 ethereal media. Thus the wave length is very great and 

 the velocity of propaga ion very small in sound as com- 

 pared with light. This se-ms sufficient to account for 

 the greater definition of shadows in light ; but when a 

 slit or an obstacle is made as narrow for light as for 

 sound, in comparison to wave length, the diffraction 

 divergence is probably about alke ; that is, the diverg- 

 ence at a linear slit in light, or between two buildings in 

 sound ; or again the shadow of a silk fibre in light and 

 a sound shadow of Bunker Hill monument, for instance, 

 are about alike considering wave length. With these 

 considerations it may be reasonable to expect incomplete 

 or only partial polarization with such apparatus as em- 

 ployed above. 



The conclusions to which we are conducted by the 

 foregoing may be summed up as follows: 



1st. That vibrations in extended media, produced 

 from the action of a remote single centre of disturbance, 

 can only be longitudinal, even in light. 



2d. That vibrations will be to some extent transver- 

 sal when due to two or more centres of disturbance not 

 in the same line, as when two or more independent co- 

 existent systems of undulations combine into one, or 

 when a simple system is modified by such lateral dis- 

 turbance as a reflection or a refraction. 



3d. That undulations, to be in a condition called 

 polarized, probably consist of vibrations which are trans- 

 versal, and that no necessity exists for assuming vibra- 

 tions transversal in front of a polarizer. 



Note. — As regards longitudinal, oblique, transversal, 

 etc., in the foregoing, the estimate is to betaken by com- 

 paring the direction of the line of vibration of a particle 

 with that of propagation of the wave. 



My acknowledgements are due to Mr. Clarence H. 

 Wright, who, while a student in my physical laboratory 

 last Spring, rendered valuable aid in the experimental 

 work. 



ASTRONOMY. 



COMET (a) l83l — SWIFT. 



The question of the best method of transmitting tele- 

 graphic announcements of astronomical discoveries has 

 just been discussed by the leading European societies, 

 and a system has been devised by which this information 

 may be comprised in a message cf sixteen words. 

 Thinking that perhaps a better way existed of doing the 

 same work, the Boston Scientific Society has adapted a 

 telegraphic code to the needs of the occasion, and this 

 system has just received a practical test. The announce- 

 ments lie within the province cf the Smithsonian Institu- 

 tion, and it was accordingly decided to transmit by cable 

 the elements and ephemeris. These here given were 

 computed at Dun Echt Observatory, in Scotland, by Drs. 

 Copeland and Lohse, and have been distributed in this 

 country to astronomers by special circulars of the Bos- 

 ton Scientific Society. That set which was computed 

 at Boston, for the Society, by Mr. S. C. Chandler, Jr., has 

 already been cabled to Europe, and distributed by mail, 

 from the Observatory of Lord Crawford, to astronomers 

 in England and the Continent. 



The cablegram received at Boston consisted of sixteen 

 words, and the translation is here appended. According 

 to the same code, the announcement of discovery could 

 be comprised in a message of seven words, which would 

 itself contain check words against possible error in 

 transmission. 



The elements and ephemeris computed at Dun Echt, 

 on Monday, May 9, were transmitted by cable to Boston 

 in the following message : " Decimosexto erective con- 

 textual bewitchery anticly demonstrative courageously 

 sputter arithmancy stomachical auriferous suety bayou 

 synecdochically bissextile eminently." The translation 

 of this message is as iollows, viz : 



ELEMENTS OF SWIFT'S COMET, l88l (rt). 



Per. Passage, 1881, May 20.67, Greenwich Mean Time. 



Long. Perihelion, 

 Long. Node, 



(J = 7T 11, 



Inclination, 

 Log. q = 9.7674- 

 Motion direct. 



Greenwich, midni 



May 10, 



14. 

 18, 

 22, 



fht. 



300 

 124 



175 - , 

 78 48 J 

 q = 5854. 



EPHEMERIS. 



, A.R. 



h. m. s. 



38 32 

 56 48 



1 17 32 

 40 48 



g > Eq. 1 881.0. 



+ 26 



is 



46 

 35 

 54 

 55 



Brightness. 

 1.69 



2.32 



Computed by Dr. R. Copeland and J. G. Lohse, from 

 observations made at Dun Echt Observatory. The light 

 at discovery is taken as unity. 



By means of control-words in the message, it is ab- 

 solutely known that the elements are those computed 

 yesterday in Scotland, and it is proposed to cable in the 

 same way the first elements and ephemerides of future 

 comets, obtainable at either terminus, until the cede has 

 been most thoroughly tested. J. Ritchie, Jr. 



