584 



NATURE 



lApril 19, 1 888 



publication is a frequent and a grossly careless error, for in every 

 case the information is forthcoming. Examples are : — 



P. 225. — Siddall, Nature, vol. xv. — instead of Annual 

 Report Chester Soc. Nat. Sci. 



P. 230. — Williamson, Nature, vol. xvii. — instead of Proc. 

 Manchester Lit. Phil. Soc. 



P. 250. — Suess, Quart. Journ, Geol. Soc, xxvi. — instead of 

 Verh. k. k. geol. Reichs. 



Moreover, the hopeless nature of his published errata may 

 indicate that the author was somewhat ashamed of his work, and 

 it is difficult to understand why the book was not stopped and 

 reprinted, before it was allowed to pass into circulation. 



Enough has now been said of the original work — that is, the 

 first attempted list ; we will now pass on to the supplement I. 

 In this, at least, we might have hoped that the compiler would 

 have profited by experience, and used more care. There is 

 certainly a difference in the proportion of typographical errors, 

 but such details as volumes are still rather wild {.Bull. Soc. Geol. 

 France, for 1886, is quoted here and there as vol. x., xiv., 

 &c.). We gather from the perusal of his supplement many 

 things we could not understand in the original work. We reco,;j- 

 nize that the compiler is neither a born bibliographer, nor 

 acquainted with scientific literature. We observe with satis- 

 faction that the words " [not seen] " occur more frequently than 

 in the earlier work, but can it be possible that the author has 

 seen a copy of Silvestri's paper noted on p. 62 ? It is exceed- 

 ingly rare, it does not exist in English libraries, and the writer 

 of' this has only seen two copies, both of which were sent to 

 him from Italy. It would have been interesting to learn the 

 pagination of so scarce a paper : the title as it at present stands 

 is strongly suggestive of a bookseller's catalogue. And surely it 

 was worth the compiler's while to quote Ehrenberg properly 

 (p. 65) while the book was presumably lying open before him ? 

 The book also is known as " Mottatsbericht" not " Verhand- 

 lungen," that is a secondary title. A very careless error is seen 

 on p. 57, where Orbilolina conoidea, Alb., and 0. discoides. Alb., 

 are quoted. The original gives Albin Gras as the authority, whose 

 paper on the subject, moreover, is well known. There should 

 not have been confusion here. On pp. 64, 65, 71, 72, and 74, 

 the same careless duplication of entries occurs as seen in the 

 first attempted bibliography. But worse than all, perhaps, is the 

 rendering of different versions of the title of one publication. 

 A good instance of this is seen on pp. 66, 67, where six variants 

 of Verh. k. k. geol. Reichs. are used, some ( Ver. K. K. Geol. ) 

 being quite unintelligible to the uninitiated. On p. 72 we see 

 two versions oi Ann. Soc. Beige Microsc, and only those familiar 

 with the book would recognize readily " Vierteljahrsschrift d. 

 Ztir. Natur. Gesellsch." (p. 74\ with its chief word abbreviated. 

 The compiler should remember that there is no necessity to 

 quote, but, if he quotes, he should quote correctly. 



It is needless to waste space on such clumsinesses as Prof. 

 Wm. King, S.C.D. (?D.Sc.) (p. 1), ox Jahrbtich. Geol. Reicht. 

 It is also advisable to have some method even in printing. The 

 compiler of this list uses roman and italics indiscriminately for 

 titles of works (p. 71, Steinmann — where more prominence is 

 thus given to the review than to the original work), while on 

 p. 6^1, in the entry Alth, the word Rozprawy begins the title of 

 the book, and has nothing whatever to do with the title of Dr. 

 Alth's paper. 



Many of these errors and defects might have been avoided had 

 the compiler been accustomed to public libraries, or even en- 

 deavoured to find out the common books of reference, always at 

 hand in these places. No bibliographer should ever think of 

 working in scientific literature without hisCarus and Englemann, 

 his Scudder, and his Bolton, and for an American to omit to do 

 so is sinful. No greater mistake was ever made by a writer than 

 that made by the compiler, when he wrote in his preface that he 

 had enjoyed facilities not enjoyed by many scientific students, 

 those facilities afforded by the great public libraries of New 

 York. We know what the resources of those libraries are, and 

 the production which calls for this letter does not shake our 

 faith in them. " Instructive" this bibliography certainly is, but 

 not in the sense intended by its compiler. 



Chas. Davies Sherborn. 



Density and Specific Gravity. 

 May I ventilate a point in mechanical definition which has 

 perplexed students within my experience — the use of the words 

 density and specific gravity? 



We are usually told that the quantity of matter in a body — as 

 it is now called, the mass of the body — is proportional to the 

 volume and density conjointly. This is Newton's definition of 

 density (see also Thomson and Tait's "Natural Philosophy," 

 § 208). Thus, if M be the mass, V the volume, and p the 

 density of a body, we have — 



M =pV 



(I) 



if the unit of mass be taken as the unit of volume of a substance 

 of standard density. 



Again, we are told -that specific gravity is the ratio of the weight 

 of the given body to the weight of an equal volume of some 

 standard substance (Besant's "Hydrostatics and Hydrodynamics," 

 § 13). Since weights are simply proportional to masses, it follows 

 that the numerical values of specific gravities and densities are 

 exactly the same. It would seem better, under these cir- 

 cumstances, to use one word only to express the one physical 

 property. Accordingly, we find that specific gravity is dis- 

 appearing from many of our best books (I think from Thomson 

 and Tait's " Natural Philosophy," for example), though it still 

 holds its place to puzzle students in examinations, and therefore 

 teachers are compelled to make the best of it they can. 



But this is not the whole evil. The definition of specific 

 gravity is usually followed by the equation — 



W = .fV (2) 



where W is the weight, s the specific gravity, and V the volume 

 of the body. This equation is, no doubt, usually accompanied 

 by the caution that the unit of weight chosen is not the unit of 

 force proper to other dynamical equations, and for this reason 

 the equation 



^ = 9^g (3) 



is far to be preferred. 



If equation (2) is of practical value, would it not be as well 

 to define specific gravity in accordance with it, and say that 

 specific gravity is the weight of unit volume of the substance ? 

 Thus, the specific gravity of water would be expressed by 

 62"5 lbs. avoirdupois in Briti>h units, or by i gramme inC.G. S. 

 units. I believe this would have the advantage of conveying a 

 perfectly definite idea to minds which dislike such abstractions 

 as mass and density. L. Gumming. 



Rugby, March 31. 



" Coral Formations." 



Mr. Mellard Reade last week (April 5, p. 535) pointed 

 out an error in my calculations which I had myself discovered 

 when too late, and had intended to correct in sending you a 

 further note on some experiments which are now in progress. 



Mr. Reade seems to make use of my arithmetical blunder, and 

 apparently attempts to discredit my experiments, and the new 

 views as to coral-reef formations ; but I leave the matter to those 

 who have a practical knowledge of the subject. 



The corals experimented upon were of the class known as hard 

 corals, and consequently the amount dissolved must be much 

 smaller, I imagine, than that dissolved from the softer varieties, 

 such as Porites. The first experiment (p. 462) gives the highest 

 result, but I have no reason to doubt that the rate of solution 

 deduced therefrom is far below that actually taking place in the 

 tropical areas of the Pacific and Indian Oceans. 



I do not consider that Mr. Reade has given an answer to Mr. 

 Irvine's pertinent question, though he would have it appear that 

 an answer is patent to everyone, and he must not take up your 

 space with such a trivial matter. 



Mr. Murray, speaking of his tow-net experiments in his Royal 

 Institution lectures, says : — " I give this calculation more to 

 indicate a method than to give even the roughest approximation 

 to a rate of accumulation of deposits. The experiments were 

 too few to warrant any definite deductions " ; and he is evidently 

 satisfied that we have no knowledge, other than relative, as to 

 the rate of accumulation of calcareous deposits. 



It is at once evident to all who have used the tow-net, that 

 Mr. Murray's experiments afford a very slender basis for calcu- 

 lations. Probably not more than one-fourth of the water in the 

 track of the tow-nets actually pass-ed through the nets, and not 

 more than one-half of the organisms that entered them were 

 retained ; the Coccospheres, Rhabdospheres, and small Fora- 

 minifera, for instance, passing through and escaping with the 



