58 



POPULAR SCTET^CE l^TEWS. 



[Al'KIL, 1S89. 



energy is transformed into the heat energy 01 

 the fire ; the heat energy is changed to force, 

 or work energy, in the boiler and engine ; 

 the work energy turns the dynamo macliine, 

 and is changed, first into magnetic energy, 

 and then into electric energy. The electric 

 energy passes out through the wires, and is 

 changed into light energy, by the arc and 

 incandescent lamps ; or, if it enters an electric 

 motor, it again goes through the changes of 

 magnetism, and work, and is finally dissi- 

 pated as the heat of friction. If the current is 

 employed in an electro-plating bath, it is 

 converted into chemical energy once more, 

 — and the circle of transformations is com- 

 plete. 



Nearly all the diflerent forms of energy of 

 which we make use in our daily life, origi- 

 nate in the chemical action of the combustion 

 of wood or coal. This we transform into 

 heat, to warm our dwellings ; into light, to 

 illuminate our cities and buildings ; and into 

 work, to turn our machinery and produce all 

 the various manufactured articles which add 

 so much to our comfort. The power exerted 

 by men and animals is transformed from the 

 chemical energy of the oxidation of the food 

 in their bodies, while the power of wind and 

 water comes more directly from the sun — 

 that great central reservoir of energy, from 

 ■ which even the energy stored up in coal first 

 had its source. Our homes are lighted by 

 the sun at night just as truly as by day, only 

 in the former case the light energy comes to 

 us indirectlv, by way of tlie coal fields, where 

 it has been lying stored up for millions of 

 Ncars, awaiting the pick and shovel of the 

 miner. 



It is also true that all these transformations 

 of energy take place according to mathemati- 

 cal laws. A pound of coal, or pure carbon, 

 will, when oxidized, or burnt, always pro- 

 duce exactly so many units of heat. From 

 this heat, just so much power or work can be 

 obtained, and no more ; this power will pro- 

 duce an invariable ninnber of imits of electri- 

 city or magnetism, and the electricity, when 

 transformed into chemical action, will decom- 

 pose a definite weight of a chemical com- 

 pound. Every pound of coal, every oimce 

 of food, represents a certain amount of energy, 

 and by no possibility can a greater amount be 

 obtained from it. It is the legitimate field of 

 the inventor to endeavor to utilize all this 

 energy in the form in which it is desired, and 

 prevent the enormous waste b)' its transforma- 

 tion into undesired forms, which at present 

 occurs even with our best and most econom- 

 ical machinery. Any attempt to do more i,'- 

 as sure to end in failure, as would an attemp' 

 to prove that two and two added together 

 make five. 



The final transformation of all energy is, as 

 far as we know, intf) heat. Every pound of 

 coal we burn, whatever forms of energy it 



may pass through, is finally converted into 

 heat, and contributes, in an infinitesimal de- 

 gree, to raising the temperature of the whole 

 univex'se. We are unable, with our present 

 knowledge, to follow it any farther, and can 

 only look forward to the final exhaustion of 

 the solar reservoir, and the cessation of 

 all light, heat, and other forms of energy, 

 as well as life itself. We can see nothing in 

 the future ages but a cold, dark, lifeless uni- 

 verse. Tliere may, however, be some undis- 

 covered law, by which the wasted heat energy 

 may be gathered up and again concentrated 

 into centers like our sun, to pass once more 

 through the same cycle of changes ; but, as 

 yet, such a law isonly a matter of specidation, 

 and belongs rather to the province of the 

 metaphysician than to that of the scientist. 

 While we know l)ut little oi tlie past, we 

 know still less of what changes the future 

 may bring in the condition of the imiverse. 



A PHOTOGRAPH OF THE TOTAL 



SOLAR ECLIPSE. 



The accompanying engraving is copied 



from La Nature, and is a reproduction of a 



photograph of the total solar eclipse of last 



and shows most beautifully, the chromo- 

 sphere, protuberances, and a part of the cor- 

 ona. Such a photograph as this is a triumph 

 of science, and would have been considered 

 impossible not many years ago. A large 

 number of equally fine photographs, both of 

 the Sim and tlie spectra, were obtained by the 

 diflerent oliserving parties, and will un- 

 doubtedly be of the greatest scientific value. 



January, taken by Professor J. A. Brashear, 

 at Winnemncca, Nevada. It com]5rises a 

 part of the southern polar regions of the sun. 



[Sjnicial Correspondence of The Popular Sclgice News.] 



I'ARIS LETTER. 

 Thk question of the general relations of animals 

 and plants is always one of great interest. The 

 great usefulness of animals to certain plants, as the 

 means through which fertilization is rendered pos- 

 sible, is well known since the researches of Ch. 

 Darwin. Onthe other hand, the plants are, directly 

 or indirectly, the source of all food to the whole 

 animal world. A superficial glance, even, shows, 

 iiowever, that all plants are not equally utilized as 

 food — that many are much demanded by animals, 

 while others seem to be considered with little favor, 

 and not to be much appreciated as food. What are 

 the reasons of these differences? The question has 

 been recently studied, in a short and incomplete 

 manner, of course, but with very interesting results, 

 by M. L. Errera, of Brussels, and by Stahl, of Jena, 

 whose works have been reviewed in the Revue 

 Scieniijiqiie, by M. H. de Varigny. M. Errera's 

 Brochure deals with the various methods through 

 which plants are protected against animals — not all, 

 of course, but a good number. These methods are 

 quite varied and interesting. Some plants live in 

 remote places, where animals cannot easily have 

 access; others live in great numbers together, and 

 protect each other mutually ; some mimic the exte- 

 rior aspect of dangerous plants ; some are possessed 

 with spines, hairs, bristles, hard bark, unpleasant 

 raphides, and cystolittoes; others contain matters 

 of unpleasant taste or smell, many of which are 

 poisonous — alkaloids and glucosides, resins, fatty 

 substances, etc. M. Errera considers alkaloids as 

 having no other function than that of protecting 

 plants against animals. Alkaloids do not seem to 

 have any use as foods, and are, most likely, dissimila- 

 tion products. That alkaloids are of use in protect- 

 ing plants— and this is true not only of alkaloids, 

 but of glucosides, and, in fact, of a quantity of sub- 

 stances which are neither alkaloids nor glucosides — 

 is shown by the experiments of M. Stahl. This 

 botanist, professor in Jena, has studied but a few 

 indigenous plants, and has studied them only in 

 view of the protection they enjoy, through one 

 method or another, against snails — indigenous 

 snails only. He has seen that all , indigenous, 

 alkaloid-containing plants are neglected by snails, 

 while the same plants, after the dangerous matters 

 have been expelled through a soaking in alcohol, 

 .ind the leaves have been thoroughly washed, dried, 

 and soaked again in water, are very willingly eaten 

 by the snails. Tannin is also a good protection 

 against these animals; leaves containing much of it 

 are generally avoided, while, after the tannin has 

 been expelled, the snails generally eat them vora- 

 ciously. M. Stahl has seen that among the fifty or 

 sixty species of plants investigated by him, in view 

 of the protection they possess against the attacks of 

 snails, not a single mild sjiecies is utterly devoid of 

 means of protection. These means vary, of course, 

 being either mechanical (hardening of exterior cells, 

 cystolittoes, raphides, bristles, .spines, hairs, etc.) or 

 chemical. Generally, mechanically protected plants 

 enjoy less protection than those that are endowed 

 with chemical defences. Some plants possess only 



