Oct. 1 8, 1877] 



NATURE 



521 



of the brick at the bottom is very much less than it would be if 

 it fell from the wall under the influence of gravity. In lifting it 

 down the man does work against gravity, and therefore the 

 energy of position of the brick on top of the wall finds its 

 equivalent (i) in the z'is viva of the brick at the bottom, and (2) 

 the mechanical value of the heat of oxidation of the man's 

 muscles working against gravity. This last is of course the 

 difference between the vis viva under gravity alone, and the 

 actual t7V viva. Plence the man wastes tissue more, digests ///i)« 

 food, and radiates more heat than if he were at rest. 



I beg to add a word upon the letter of" X." concerning the term 

 potential energy. Used as the term is to denote energy of 

 position, it cannot be considered " felicitous " or logically exact. 

 Energy of position is /o.V;;//!// z'/j rvew (or kinetic energy); and 

 vis viva (against a force) \s potential energy of poiilion. In the 

 expression potential energy, we are led to inquire which energy. 

 As it stands it properly implies the idea of possible vis viva, as 

 if "energy" was used only to signify vis viva or kinetic energy. 

 It may be noticed that Prof, llelmhollz uses vis viva for 

 "energy " (the adjectives actual and latent being understood) in 

 two places ; viz., in his tract on " Conservation of Force," p. 128 

 of translation, "The CTjTTOaof asingle particle Aw, &c.," and in 

 "Popular Lectures," p. 196, trans., "The vis viva of motion of 

 revolution round the sun, &c.," where the algebraic expression 

 given shows that the whole vis viva, actual and latent, or, as it is 

 DOW called, the whole energy, kinetic and potential, is meant. 

 While then the German philosopher uses vis viva for work-power 

 in general, the English writer in the terms potential and actual 

 energy employs adjectives which logically require that energy 

 should signify only work-power of motion. Out of this maze 

 " X " suggests a way by proposing to use the term " energy of 

 tension " for potential energy, with a reminiscence of Helmholtz's 

 " .Sum of the tensions ; " but if we keep the expression kinetic 

 energy, we require a corresponding adjeetive to distinguish the 

 other form of energy, and what more expressive, more exact, 

 more " felicitous " word could we find than " statical," the word 

 originally employed by Sir W. Thomson? We have here a 

 most appropriate word, supported by a great name, and I venture 

 to suggest that "st.itical energy" should come into general use. 



Arnesby Vicarage, Rugby W. P. O. 



Dealers in Zoological Specimens and Models 



II.WING had a considerable amount of trouble in ascertaining 

 the addresses of the various dealers in zoological specimens in 

 this country and abroad, I think it likely that I may be doing 

 service to others who like myself are charged with the formation 

 of an educational museum of zoology and comparative anatomy, 

 if I give in the columns of Nature a complete list of such 

 dealers as I have found useful. They are as follows : — 



1. For spirit specimens and dried parts of fish, molluscs, insects. 



corals, (Sec. — Cutter, Bloomsbury Street, London. 



2. For skeletons, &c., Ed. Jerard, jun., College Place, Camden 



Town, London. 



3. For Ceratodus, insects, iS:c. — Hig^ins, 22, Bloomsbury Street, 



L jndon. 



4. For molluscs, and various marine forms — R. Damon, 



Weymouth. 



5. For American fish and amphibians — Prof. Henry Ward, 



Rochester, New York. 



6. For skeletons of fish, iScc, &c. — Erber, 7, Sigmundgasse, 



Vienna. 



7. For skeletons and exotic specimens generally — Gustav 



Schneider, 67, Grenzackeslrasse, Basel. 



8. For exotic specimens generally — Museum Godeffroy, 



Hamburg, 

 g. For Mediterranean fish, molluscs, &c. — Gal, fieres, I, 

 Maritime, Nice. 



10. For glass models of invertebrates — Blaschka, 9, Schiesgas;e, 



Dresden. 



11. F>ir wax models of anatomy of parasitic worms and of 



vertebrate anatomy and embryology — Weisker, 13, 

 Thalstrasse, Leipzig. 



12. I'or wax models of vertebrate and invertebrate embryology 



— Dr. Ziegler, Freiburg, Baden. 



13. For live starfishes, Myaarenaria, Cyclopterus, and other 



forms — J. Thompson, 11, York Place, Southend, Essex. 



14. For anemones, and channel maiiiie fauna — R. T. Smith, 



25, St. Alban's Street, Weymouth. 



I trust that some of your correspondents will enlarge this 

 list, and that such as it is it may be of use. 



E. Ray Lank ester 



Ornithology of Costa Rica 



In Nature, vol. xvi. p. 446, I see that you announce my 

 return to this country. I take the hberty of rectifying two 

 errors in the announcement : — ist. I was five months collecting 

 in Costa Rica (not four months), from the end of December to 

 the end of May. 2nd. I have brought home 250 species (not 

 200), and it may interest your readers to know that among these 

 250 species, besides the female of Carpcdectes niliJtts, are also 

 some other very rare birds many of which — one or other of the 

 sexes — are new to science. I add a list of some of them in case 

 you may feel disposed to give it in your journal. 



Odontophorus guttatus (Gould), Dendroityx leiieophiys (Gould), 

 Geotiygon costaricensis (Lawr. ), Tonurus hoffmanni (Cab.), 

 Tetragonops frantzii (SclsX.), Tuidus nigrescens [C^^.), Tnrdus 

 obsoletus (Lawr.), Catharus frantzii (Cab.), Cathariis ^raeili- 

 ros'.ris (Salv.), Dcndraeca vicilloti (Cass.), Setophaga torqiiata 

 (Baird), Phainoptda melanoxantha (Salv.), male and female 

 (just described by Mr. Salvin, from a single specimen, 

 sex unknown, sent by Mr. Rogers), Chlorophonia callophrys 

 (Cab.), Pezopetes eapi/alis (Cab.), Pyrgisoma cabanisi (Sclat. 

 and Salv.), J'yj-gtsoma leueotis (Cab.), Eugenes sfeetabilis 

 (Lawr.), both sexes, Oreopyra hemileuca (Salv.), Oreapyra 

 einereicauda (Lawr.), Selasphorus flammula (Salv.), both 

 sexes, Panterpe insignis (Cab.), ditto, and several new species 

 belonging to the families Fringillidce, Trochilid,e, and Tyra- 

 nidtc, of which I am preparing a description, as well as a 

 general list of all the species collected by me (with notes on 

 many of them), for publication in the Proceedings of the Zoological 

 Society. A. BoUCARU 



55, Great Russell Street, W^C. 



On the Supposed Influence of Light on Combustion 



Bei'ore Dr. Ingleby referred to my experiments as "incon- 

 clusive," his reference should at least have been accurate. He 

 says that I " actually used a dark cubbard into which there was 

 no free influx of atmospheric air." So far from this being the 

 case, the "dark closet," as I call it in my paper, was the photo- 

 meter-room of Price's Candle Company, an enclosure 12), feet 

 long, 3J. feet wide, and 6i feet high, with arrangements for con- 

 stant ventilation both at the bottom and at the top. So far 

 from candles "naturally burning there with inferior combustion," 

 as Dr. Ingleby supposes, it is in constant use for testing the 

 burning of candles, and any deficiency in the supply of air 

 would be shown quickly by the production of smoke, and yet 

 after being so used for many hours there is not a trace of smoke 

 in the air. 



Dr. Ingleby's assumption that the candles burnt with inferior 

 combustion in the closet is in direct opposition to the statement 

 made in my paper. In the first and fouith trials there is a 

 greater consumption in the light than in the dark ; and in the 

 second and third trials the consumption is gi eater in the dark 

 than in the light; but in any case the difference is so small, 

 amounting only to from two to seven grain; per hour, that it may 

 fairly be referred to slight differences in temperature, in currents 

 of air, and in the composition and make of the candles — the 

 etcteris paribus ■vi\{k\\ Dr. Ingleby, with unnecessary emphasis, 

 says I " left entirely out of the experiment." 



The method adopted by me has the advantage of measuring 

 the results by aetual weighing, and I attach no importance to 

 any opinion that is not founded on a similar basis. I cannot 

 follow Dr. Ingleby's theory. What does "insidious eclipsing 

 the waning glimmer of expiring embers," mean ? I can under- 

 stand that sea-coal — a caking coal — may form hard cakes, 

 below which the fire burns out unless the cake is broken, an 

 action which does not occur with non-caking coals such as a 

 great part of the Staffordshire and Lancashire co.als, but I can- 

 not see why if the " last faint gleam is invisible " in consequence 

 of a brighter light, therefore "the fire goes out as a matter of 

 course." That the sun puts out the fire by rarefying the air 

 necessary for combustion I take to be pure fiction. 



In my experiments differences of temperature were slight. If 

 there was any difference one would expect the temperature to be 

 higher in the closet than in the open room, but in the fourth trial 

 the temperature in the .-junshine was the higher. If the candle 



