POP ULAR MIS CELL ANY 



833 



Sir John Herschel, and he gave the explana- 

 tion that hydrogen breaks the continuity of 

 the medium. But this is not the true expla- 

 nation. Professor Stokes, paying attention 

 to the fact that when a tuning-fork is struck 

 and held in air it gives out but little sound, 

 investigated the subject, and arrived at the 

 conclusion that air is so mobile that it runs 

 around the tuning-fork without being thrown 

 into waves. Check this " running round" 

 by holding a card at one side of the fork, 

 and the sound is augmented. Xow, hydro- 

 gen is more mobile still than air, and hence 

 the probable explanation of the bell not 

 sounding in it is, that the hydrogen " runs 

 round " so readily that it is not thrown into 

 waves. Alluding to Newton's attempt to rec- 

 oncile his theoretical calculation of 916 feet 

 per second with the experimental results of 

 1,090 feet per second as the velocity of 

 sound. Professor Tyndall said that the phi- 

 losopher had forgotten to take into account 

 the heat developed by the sound-wave in its 

 own path. By the aid of the thermopile 

 and galvanometer arrangement, the lecturer 

 showed that a very gentle and small com- 

 pression of air does produce heat. Several 

 experiments to show the passage of sound 

 through wood, water, and other bodies were 

 made in the concluding part of the lecture. 

 In one of these experiments music played in 

 the cellars of the Institution was made audi- 

 ble by a connecting wooden rod rising into 

 the lecture-hall, a common wooden tray be- 

 ing alternately held on the top of the rod 

 and removed again. The rod itself had not 

 surface enough to give vibrations which 

 can be heard, but the larger surface of the 

 tray gave the " magic music." 



An ingenious and very simple method of 

 measuring the velocity of sound in air and 

 other gases is described by M. Bichat, in 

 the " Journal de Physique." A tube about 

 ten metres long, made of tin plate, is bent 

 so that its extremities A and B are near to- 

 gether. The end A is closed by an India- 

 rubber membrane ; the end B carries a cork 

 with a glass tube through it, which com- 

 municates, by means of an India-rubber 

 tube, with a Marey's raanometric capsule. 

 These capsules are arranged in front of a 

 blackened cylinder, so that the extremities 

 of their levers rest upon the same generating 

 line. Close by these a tuning-fork, making 



one hundred vibrations per second, is placed, 

 and inscribes its vibrations side by side 

 with those of the manoiuetric capsules. 

 The experiment being so arranged, a slight 

 shock is given by the hand to the mem- 

 brane A, the blackened cylinder meantime 

 being turned. The capsules register the 

 point of departure and the point of arrival, 

 while the tuning-fork gives the time. In 

 this way the velocity of sound in air was 

 found by M. Bichat to be 333.3 metres per 

 second. By means of two tin tubes, placed 

 one above the other, we may in a single ex- 

 periment demonstrate the difference of ve- 

 locities of sound in air and in hydrogen ; 

 but it is difficult, in consequence of diffusion 

 through the India-rubber, to keep the tube 

 full of pure hydrogen. 



Recent Exploration of Wyandotte Cave. 



— Wyandotte Cave, in Crawford County, 

 Indiana, has a total length of twenty-three 

 miles, including all the avenues ; it includes 

 many fine halls and domed chambers, the 

 largest of which has a circumference of one 

 thousand feet, and is said to be two hundred 

 and five feet high. The Rev. H. C. Hovey 

 mentions, in " The American Journal of 

 Science," an important discovery made in 

 this cave last April by a party of students 

 from Wabash College. Forcing their way 

 through a low, narrow passage from the 

 locality known as Rugged Pass, the party 

 entered a realm of chaos. " Pits, miry 

 banks, huge rocks, are overhung by galler- 

 ies of creamy stalaetite, vermicular tubes 

 intertwined, frozen cataracts, and all, in 

 short, that Nature could do in her wildest 

 and most fantastic mood." One of the cu- 

 riosities of this place is a row of stalactites 

 on which a musical chord can be struck or 

 a melody played. What is known as the 

 " Old Cave " was worked by saltpeter miners 

 in 1812, and sundry acts of vandalism have 

 been charged on them which more probably 

 were done by the aborigines. The finest 

 stalacto-stalagmitic column probably in the 

 world is the Pillar of the Constitution in 

 this " Old Cave." It is forty feet high, 

 twenty-five feet in diameter, and it rests on 

 a base three hundred feet in circumference. 

 The weight of this immense mass of ala- 

 baster caused the underlying rocks to set- 

 tle, and this in turn cracked the base, cans- 



