540 



SCIJENGE. 



[Vol. VI., No. 150>. 



unless the sirup be put into the cans in a very watery 

 condition, the formation of a thick layer of crystals 

 at the bottom invariably follows ; and I have often 

 seen great difficulty experienced in removing it with- 

 out breaking the cans. J. Edward Chappel. 

 Warsaw, N.Y., Dec. 14, 



International geological congress at Berlin. 



On referring to the original notes which I took 

 during the sessions of the International geological 

 congress, I find that Mr. Archibald Geikie moved to 

 strike out all the words after ' Coudroz ' except 

 ' rOld Eed,' in the paragraph (1. c, p. 15) of the re- 

 port of the committee on uniformity of nomenclature, 

 my account of which Dr. Dewalque criticises in Science, 

 Dec. 11. Upon this, M. Renevier asked, 'on princi- 

 ple,' that the whole paragraph be struck out, on the 

 ground that the congress ought not to go into such 

 details. There is no mention in my rough notes that 

 this was done ; but in the fair copy, which I submitted 

 to some of the leading members of the congress for 

 their approval or correction, I find a pencil note to 

 the effect that M. Eenevier's motion was carried. I 

 cannot recall the authority for this note, which was 

 embodied in the short summary which, with the 

 assistance of Professor Williams, I prepared for S'ctence. 

 I should like to state here, that in spite of the em- 

 ployment of the greatest possible care, and the assur- 

 ances of the accuracy of the account of the meeting, 

 which is about to appear in the American journal of 

 science and arts, from some of the most active par- 

 ticipants in the discussions, some errors, though I 

 trust none of importance, will probably be found. 

 To those who are aware of the exceedingly inferior 

 acoustic qualities of the hall, and the involved nature 

 of some of the discussions and votes, these will be 

 thought pardonable. Peesifor Frazer, 



Philadelphia, Dec. 12. 



Earthquake-shocks more violent on the surface 

 than in mines. 



It has been sometimes observed that earthquake- 

 shocks are felt more severely in mines than at the 

 surface. This may be accounted for partly by the 

 rapid decrease of the shock-motion (wave-height) 

 which is supposed to vary inversely as the square of 

 the distance from the focus or radius of the agitated 

 sphere, partly by the quenching of the earth-wave by 

 repeated reflections in passing through media of dif- 

 ferent elasticities, and by the fracturing of the im- 

 perfectly coherent media through which it passes. 

 But the converse phenomenon, viz., the greater 

 severity of shocks on the surface than in mines, is, I 

 believe, far more common. This was very conspicu- 

 ous in the Inyo earthquake of 1872 ; for buildings 

 were shattered and the earth was broken in many 

 places, and yet persons working in the mines were 

 scarcely aware of any movement. The same has 

 often been observed in Peru. 



There are two ways in which I imagine this may 

 be explained. The more obvious is as follows : As 

 long as the earth-wave is within the earth, the back- 

 and-forth movement (shock-movement) is largely 

 restrained by the work of elastic compression of the 

 earth in front necessary for the progress of the wave. 

 But as soon as it reaches the surface the motion is 

 free or unresisted, and therefore much more rapid, — 

 so rapid as often to break up the surface, and throw 



loose lying bodies high into the air. But there i» 

 another explanation which is perhaps more doubtful ^ 

 and which, therefore, I offer with some hesitation as 

 a mere suggestion, in the hope that some one may be 

 able either to follow it up or else to disprove it. 



In the Philosophical magazine of June, 1849, p, 

 404, the royal astronomer. Professor Airy, drew at- 

 tention to the peculiar phenomena of what he calls 

 broken waves, or broken-headed waves. These are 

 retarded, discontinuous waves ; in other words, break- 

 ers. If a normal wave strike against a sea-wall, 

 it will of course be reflected ; but if a breaker, a 

 broken or broken-headed wave, thus strike, the 

 swell or unbroken part is reflected as usual, but the 

 broken part is not. If it strike perpendicularly, the 

 broken part is thrown up and destroyed. If it 

 strike at small angle, then the broken part runs along 

 as a strong wave clinging to the surface of the walL 

 I have myself observed this behavior of broken 

 waves. 



Professor Airy then applies this principle to the 

 explanation of certain phenomena of whispering- 

 galleries. The voice produces normal waves ; but a 

 hiss, a buzz, and therefore a whisper, produce 

 broken, discontinuous waves. Now, in these gal- 

 leries the voice is reflected in the ordinary way ; but 

 a whisper runs along, clinging to the surface of the 

 wall and dome, and may be heard, if the ear be 

 applied to the wall, at much greater distance than 

 the much louder voice. 



Now, may not this principle be applied also to 

 earthquake- waves ? 1°. The surface of the earth 

 must be regarded as a very perfect reflection for 

 waves emerging from below ; as much so, in fact, as 

 for sound-waves entering the earth from the air. 

 Therefore normal waves emerging on the surface 

 must be largely reflected back into the earth again. 

 2°. But earthquakes are pre-eminently broken, re- 

 tarded, discontinuous waves. Passing, as they do, 

 through an imperfectly elastic and slightly coherent 

 medium, which is fissured and crushed at every step 

 of its progress, the normal continuity of the waves is 

 destroyed, and the waves retarded and their energy 

 dissipated, by change into other forms of force, 

 especially heat. For this reason the velocity of 

 heavy earthquake-waves is always much less than 

 that of normal elastic waves in the same medium. 

 For this reason, too, they are rapidly quenched, and 

 therefore extend much less distance than they other- 

 wise would. 3° . If, then, we assume that earthquake- 

 waves are broken and retarded waves, they ought to 

 follow the law pointed out by Professor Airy. When 

 they strike full on the surface, as at the epicen- 

 trum, they simply destroy themselves by the work of 

 breaking the surface, and are not reflected. When 

 they strike at small angle, as at a distance from 

 epicentrum, they must run along as a strong wave 

 clinging to the surface. Joseph Le Conte. 



Berkeley, Cal., Dec. 5. 



An unreliable treatise on disinfectants. 



That ' unreliable treatise on disinfectants ' criti- 

 cised by you Dec. 4, deserves even less mercy than 

 you have shown it. When the publisher declares 

 that there is no indorsement of the essays as scien- 

 tific, and the one selected as the best is chosen as 

 a standard of the excellence of the work as a whole, 

 all persons in the least familiar with the present 

 position of sanitary science must wonder why the 



