37o 



SCIENCE. 



not be found. Since the only method in which its origin 

 can be absolutely shown cannot be used without expen- 

 sive excavation, it only remains to give the probabilities 

 so lar as ascertainable from the mass itself. Such micro- 

 scopic characters and mineral association have been, so 

 far as we know, only found in eruptive rocks when the 

 origin of such rocks has been studied with sufficient 

 care to determine it. Hence we must conclude it is 

 most probable that this mass is eruptive also, until found 

 to be otherwise. 



It closely resembles in structure and composition 

 some of the meteorites, except that its iron is oxidized 

 and not in a native state — a resemblance which for 

 others of the peridotites has long been pointed out. 

 It is rocks of this character, as has been suggested by 

 others, that give us the most probable clew to the inte- 

 rior composition and structure of the earth. 



The rock in the field shows, to our mind, no signs of 

 structural planes that should be referred to sedimenta- 

 tion. On one side the rock is massive and jointed, and 

 on the other it is jointed in fine parallel Dlanes. This 

 portion of the rock is more highly metamorphosed than 

 the other, and, as is usual in highly altered eruptive 

 rocks, joints parallel to certain lines of pressure occur. 

 The writer has seen this structure in many rocks that 

 were indisputably eruptive, forming well marked dikes in 

 other rocks. 



A rod away from the main mass of the iron ore, near 

 one end, some serpentine appears that cannot be di- 

 rectly connected with the other peridotite. Microscopi- 

 cally its characters and structure are the same as the 

 main rock, and there is no reason to regard it as distinct. 

 The rock nearest to the peridotite is a mica schist some 

 hundred feet away. It shows no characters that would 

 indicate the transition of the ore into it. 



The locality was visited bv the writer in October last, 

 in company with Professor A. S. Packard, Jr., of Brown 

 University, and Mr. T. S. Battey, of the Friends' School, 

 Providence, R. L To the latter gentleman I am espec- 

 ially indebted for a copy of the paper of the Rhode 

 Island Society before mentioned, and for other favors. 



This examination may serve as an illustration of the 

 aid that microscopical lithology may be to the practical 

 side of life, since now, for the first time since this rock 

 has been worked, can the ironmaster who wishes to use 

 it approach understandingly the metallurgical problems 

 it presents ; whether he desires to employ the rock as a 

 whole, or to concentrate the magnetite first. 



In direct-vision spectroscopes the number of prisms in- 

 volves a considerable loss of light. M. Zenger now uses a 

 liquid prism of ordinary form, having attached on its ante- 

 rior plane a quartz prism of the same refringent angle, but 

 arranged in opposite direction. The posterior face of the 

 liquid prism carries a plane parallel plate. The rays fall 

 normally on the quartz. The loss of light is by this arrange- 

 ment reduced to a minimum. The spectra obtained are 

 very intense, and the lines are well defined. A single par- 

 allelepiped of the kind decomposes the D line to the naked 

 eye, and with a small Galilean telescope, magnifying five 

 times, one can distinguish the difference of breadth of the 

 two lines, and easily see the extreme red and ultra-violet 

 rays, though there arc only two prisms of 60 degrees. 



M. Poi.iakoit, the distinguished Russian naturalist, has 

 examined a horse presented by Colonel Prejvalsky to the 

 St. Petersburg Academy, and decides it to be a new species, 

 which he has named Equus Przewahkii. A translation of 

 his memoir appears in the "Annals of Natural History," 

 and from this it appears that the new representative of the 

 family of undivided-hoofed mammals is in some respects 

 intermediate between our domestic horse and the wild ass, 

 but it differs from the asinine genus in having four callosi- 

 ties, one on each leg. In the form of skiill, absence of 

 dorsal stripe, and other particulars it resembles the domestic 

 horse. This newly-recorded animal is indigenous to the 

 plains and deserts of Central Asia, and has not hitherto 

 fallen under the dominion of man- 



COMET (b), 1881. 



We continue the interesting series of sketches of this 

 comet, made by Professor Edward S. Holden with the 

 15-inch equatorial at the Washburn Observatory, Madi- 

 son, Wisconsin. 



July 13, 1881. 



£MHr 



Figure i. 



July 14, 1881. 



ioh. 20m. 



July 17, 1881. 



July 18, 1881. 



Figure 4. 



The nucleus is DOUBLE (it has not been previously) 

 p — 275 ±, s = r.5, with a dark space between the 

 parts. 



DO WE SEE NON-LUMINOUS BODIES BY RE- 

 FLECTED LIGHT? 

 By A. G. Gaines, Pres. St. Lawrence University, Canton, N. Y. 



All who have treated this subject have answered the 

 above question with an unequivocal yes. 



It may appear presumptuous to call the answer in ques- 

 tion. Nevertheless, while reflecting recently on some of the 

 peculiar facts of light and vision the thought came to me to 

 doubt this universally accepted proposition ; and now I 

 wish to express my more confirmed doubts, and give some 

 reasons for thinking we must revise our views on this 

 point to some extent. 



What I now hold is that neither transmitted nor re- 

 flected light reveal to us in vision either the body trans- 

 mitting or the body reflecting, but that radiant light does 

 reveal in vision the radiant body, and that the light by 

 which any non-luminous body is visible is essentially of 

 the nature of radiant light, and is properly to be so called. 

 Paradoxical as these views may seem on bare statement, I 

 think that a little consideration of the facts involved will 

 soon convince us that they must be accepted as true, and 

 show us that the present paradox is clue to the illusions of 

 an erroneous point of view. 



It is a known and universally accepted truth that trans- 

 mitted light does not reveal the transmitting medium. It 

 may be refracted, little or much, but when it reaches the 

 eye it reveals, not the refracting medium, but the body 

 from which it was emitted. The refracting or transmit- 

 ting body may be visible, but is not visible bv transmitted 

 light. Were it perfectly transparent, that is", were it to 

 transmit all the light coming to it, it would be invisible. 

 This is no new truth, but one universally held and taught ; 

 and thus far we are all agreed. 



