38o 



THE POPULAR SCIENCE MONTHLY, 



utes, and then cautiously crawls about the 

 jar with antennae extended. On approach- 

 ing the piece of meat, and before touching 

 it, the animal gives a powerful backward 

 jump and remains quiet for a while. It 

 often repeats this three or four times before 

 touching the food, and when it does touch 

 it the result is another backward jump. 

 When it has become satisfied that there is 

 no danger, it takes the morsel in its claws 

 and conveys it to its mouth. " I have twice," 

 says the author, " seen the meat dropped as 

 it was passed along the base of the antennae, 

 as if the sense of smell, or more delicate or- 

 gans of touch seated at that point, were 

 again the cause of alarming the animal. 

 When the jaws once begin to work, the 

 piece of meat, or bread, if very small, is 

 devoured, but if too large, only a few bites 

 are taken, and the food is dropped and not 

 touched again." 



A detailed account is given ofoneof the 

 specimens, in order to show the mode of 

 reproduction of lost members. This speci- 

 men, a female, was captured November 13th, 

 being then perfect in all respects, except 

 the right, large claw, which was as yet ru- 

 dimentary. Total length of the animal from 

 tip of large claw to end of tail, not quite 

 two and a half inches. From November 

 14th to 24th, the crawfish lost in battle most 

 of her antennae, the third, fourth, and fifth 

 legs from the left side, the fifth from the 

 right side, and the two end-joints of the 

 third leg on the right side ; January 28th or 

 29th she cast her shell and came forth with 

 a soft white covering, which was nearly two 

 weeks in hardening. All the legs which were 

 perfect before were now of the same size, but 

 in addition the great claw of the right side 

 was developed to about one-half or two- 

 thirds the size of its fellow, and was appa- 

 rently of as much use. The two missing 

 joints of the third leg on the right side were 

 also developed, though not quite to their full 

 proportions. The fifth leg on the right side, 

 and the third, fourth, and fifth of the left 

 side, were reproduced, but in a very small 

 and rudimentary manner. The antennae 

 were about tv^o-thirds their full size. On 

 April 20th the shell was again cast ; the 

 crawfish had now all the legs and claws 

 nearly perfect. The great claw of the right 

 side was very nearly as large as that of the 



left. The tip of the third leg of the same 

 side was perfect, and all the legs that be- 

 fore were rudimentary were now developed 

 apparently to their full proportionate size, 

 with the exception of the last on the right 

 side. Antenna about full length. 



From these observations, it will be seen 

 that the parts are not reproduced in per- 

 fection on one shedding of the shell, but 

 that each time the shell is cast they are 

 more nearly perfect than before. 



Sound and Fog Signals. Among the pa- 

 pers read at the Philadelphia meeting of the 

 American Academy of Sciences, was one by 

 Prof. Henry on " Sound and Fog Signals," 

 of which we present an abstract. The au- 

 thor stated the results of experiments made 

 last summer, under the direction of the 

 Lighthouse Board, at Block Island, and at 

 Little Jail Island, at the east end of Long 

 Island Sound. One set of experiments was 

 made to investigate the cause of an echo 

 apparently heard from the ocean : the re- 

 sults were not such as to solve the problem, 

 though they favored the hypothesis that the 

 echo was due rather to a reflection from the 

 waves than from the air. Another set of ex- 

 periments was directed to investigating the 

 effect of elevation on the hearing of sound ; 

 the result was to show that a sound travel- 

 ing against the wind is heard farther away 

 on an elevation than at the sea-level. In 

 five cases, sound was heaid five times far- 

 ther with the wind than against it, the wind's 

 velocity being about five miles per hour. 

 The effects of sound traveling with the wind, 

 against it, at right angles to it, etc , were 

 shown in diagrams representing curves of 

 audition. In still air these curves are near- 

 ly circular ; with wind uniform in velocity 

 throughout the whole space the curves are 

 approximately elliptical. The curves dif- 

 fered according to the different conditions. 

 It appeared to be demonstrated that sound 

 is heard farthest with a moderate wind, and 

 that with a strong wind it is heard a less 

 distance in every direction than in still air, 

 and perhaps to a less distance than with a 

 wind of moderate velocity. These experi- 

 ments will be resumed next summer. 



Origin of the Jfnmerals. Having never 

 met with any explanation of the origin of 



