304 



SCIENCE. 



THE CONSERVATION OF ELECTRICITY. 



The following is from the preface to " Elementary Les- 

 sons in Electricity and Magnetism," by Silvanus P. 

 Thompson, now in the press. 



"The theory of electricity adopted throughout is that 

 electricity, whatever its nature, is one, not two. That this 

 electricity, whatever it may prove to be, is not matter, and 

 energy j that it resembles both matter and energy in one re- 

 spect, however, in that it can neither be created nor de- 

 stroyed. The doctrine of the Conservation of Matter, es- 

 tablished a century ago by Lavoisier, teaches us that we 

 can never destroy nor create matter, though we can alter its 

 distribution and its forms and combinations in innumerable 

 ways. The doctrine of the Consen<ation of Energy which 

 has been built up by Helmholtz, Thomson, Joule, and 

 Mayer during the last half century teaches us that we can 

 neither create nor destroy energy, though we may change it 

 from one form to another, causing it to appear as the 

 energy of moving bodies, as the energy of heat, or as the 

 static energy of a bod)' which has been lifted against gravity 

 or some other attracting force into a position whence it can 

 run down, and where it has the potentiality of doing work. 

 So, also, the doctrine of the Conseivation of Electricity, 

 which now is growing into shape, but here first enunciated 

 under this name, teaches us that we can neither create nor 

 destroy electricity, though we may alter its distribution — 

 may make more to appear at one place and less at another — 

 may change it from the condition of rest to that of motion, 

 or may cause it to spin round in whirlpools or vortices 

 which themselves can attract or repel other vortices. Ac- 

 cording to this view all our electrical machines and batteries 

 are merely instruments for altering the distribution of 

 electricity by moving some of it from one place to another, 

 or for causing electricity when heaped up in one place to do 

 work in returning to its former level distribution. Through- 

 out these lessons the attempt has been made to state the 

 facts of the science in language consonant with this view ; 

 but rather to lead the young student to this as the result o* 

 his study than to insist upon it dogmatically at the outset.' 



A WATER CARRYING TORTOISE. 



At a meeting of the Academy of Sciences the other even- 

 ing, a very fine specimen of the desert land tortoise, from 

 Cajon Pass, San Bernardino county, California, was re- 

 ceived. The specimen had been carefully prepared, and 

 was as large as an ordinary bucket. The tortoise is a native 

 of the arid region of Calilornia and Arizona, and Prof. E. 

 T. Cox, who was present, related a curious circumstance 

 connected with it. 



He found on dissecting one of them that it carried on 

 each side a membrane, attached to the inner portion of the 

 shell, in which was about a pint of clear water, the whole 

 amount being about a quart. He was of the opinion that 

 this water was derived from the secretions of the giant 

 barrel cactus, on which the tortoise feeds. This cactus 

 contains a great deal of water. 



The tortoise is found in sections of country where there 

 is no water, and where there is no vegetation but the cac- 

 tus. A traveler suffering from thirst could, in an emer- 

 gency, supply himself with water by killing a toitoise. 

 They are highly prized by Mexicans, who make from them 

 a delicious soup. The foxes of the desert attack the tor- 

 toise and finally overcome them by dragging them at times for 

 miles. 



B. B. Redding said he would try to obtain a live one for 

 the Academy in order that its habits and peculiarities may 

 be carefully observed and noted. He instanced being on 

 the Gallapagos islands in 1849 ar, d assisting in the capture 

 of 92 land tortoises, varying from 450 to 600 lbs. in weight, 

 which the vessel brought to San Francisco and sold for 

 more money than the whole cargo of lumber netted at that 

 time. They were two months on board the vessel, yet ate 

 nothing and those killed had in them considerable quanti- 

 ties of pure water. They live on the high lava rocks, which 

 rise as mountains on the island, where there are no springs 

 or streams, and the only dependence of animal life for 

 water is necessarily upon the irregular and uncertain rain 

 showers. 



It may be mentioned that the tortoise are of different spe- 

 cies, though they may have the same habit in respect of 

 carrying water. The famous edible species of the coasts 

 of the Pacific and Indies, of which the headquarters is at 

 Gallapagos islands, is the Testudo Indica. They grow to 

 five, six, and even seven hundred pounds or more. Those 

 found in this State are smaller and are the Agassii species 

 first described some years ago by Dr. J. G. Cooper, if we 

 recollect aright. Those Mr. Redding describes lrom the 

 Gallapagos were offered water while on the ship but refused 

 it. Yet when killed they all contained water. The place 

 they inhabit is a dry one, lacking water. It may be that 

 they go to the high places and obtain it from the vegetation, 

 the same as our species does. 



Daltonism. — A Belgian Commission is making investi- 

 gations on Daltonism. Their method of procedure is as 

 lollows: — On a table exposed to the bright sunlight are 

 placed skeins of wool varying in color. The subject under 

 examination is given, for example, a green colored one 

 and he is told to select another of the same color. If he 

 does so without hesitation, he is not affected with Dalton- 

 ism, but he is still subjected to other trials, as for instance, 

 the observation of colored signals at a distance. This ap 

 plies especially to those employed on railways. 



New Recording Apparatus of Movements. — About 

 twenty years ago M. Marey proposed to inscribe the differ- 

 ent movements of living animals by means of a lever, as 

 light as possible, and protected from every cause tending to 

 set it in vibration, Since this epoch a considerable num- 

 ber of operations have been accomplished by the aid of this 

 instrument ; thus, the phenomena of the circulation of the 

 blood, of respiration and of the movements of the heart 

 have, in the employment of this method, been conclusively 

 solved. Nevertheless one objection has been raised 

 against these instruments : in the sometimes excedingly 

 complicated tracings of physiological acts, the proper 

 movements of the lever have increased the real curve of 

 the movement which is to be inscribed. M. Marey has 

 therefore invented and presented to the Academy a new in- 

 scriptic apparatus, the lever being reduced, which gives 

 microscopic inscriptions, and thus can inscribe rapid 

 movements with the greatest precision. The tracings of 

 this instrument, which may be produced by the vibrations 

 of the voice, or by the breath, are afterwards enlarged by 

 projection and reduced to the necessary size. The micros- 

 copic inscription given by the new apparatus extends to an 

 almost indefinite degree phenomena susceptible of registra- 

 tion. 



FLUORESCENT SUBSTANCES. 



Substance. 



By transmitted 

 light. 



Magdala red 



Induline (acid sol.) 



Nigrosine (acid sol.) I 



Tri-sulpho-acid of induline. . . .] 

 Resorcin (di-azo compound)*. . 1 

 Resorcin (di-azo compound)*. . 

 Resorcin (di-azo compound). . . 

 Resorcin (phthalic acid com-' 



pound)* 



Resorcin (phthalic acid and 



bromine compound) j 



Amido-phthalic acid 



Murexide (di-azo compound). 



Beta-naphthole 



Naphthalamine* 



Fluoresces. 



Red 



Red 



Dirt)' green 



Red 



Dirty green 



Red 



Blue 



Red 



Yellow 



Vermilion 



Violet red 



Vermilion 



Green 



Dark red 



Yellow 



Green 



Red 



Green 



Colorless 



Green 



Yellow 



Green 



Brown 



Blue 



Colorless 



Violet-blue 



The four marked * are the best for exhibition purposes, 

 the last surpassing sulphate of quinine. The fluorescence 

 of the di-azo resorcin compound in direct sunlight shows a 

 fluorescence not inferior to vermilion paint in brilliancy. 



Sidney Jewsbury. 



