226 



SCIENCE. 



[Vol. X. No. 2. 



Some of my first slides I find useful to this day, and every day adds 

 ■experience, or a word from some friend working in tlie same field. 

 The difficulty of making sections is a myth. 



Cambridge, Mass., Oct. 31. AUG. F. FOERSTE. 



Search for Gems and Precious Stones. 



In reference to the interesting article of Prof. P. L. Simmonds on the 

 search for gems and precious stones, read before the Society of Arts 

 of England recently, reprinted in your issue of Oct. 14, allow me to 

 suggest a few corrections. Professor Simmonds estimates the yield 

 of the Brazilian diamond-mines at ^800,000 annually, while a little 

 later on he says that the yield has dwindled to 24,000 carats, which 

 •at the outside will not yield more than £2 to ^^3 a carat, and that of 

 India, Borneo, and Australia at ^200,000, when these latter figures 

 would probably cover the annual product of Brazil as well as that 

 of the other three countries named. Australia produces so very 

 little as scarcely to be a factor in the computation. Even before 

 the opening of the African mines, in 1867, the estimated value of 

 the product of Brazil from 1861 to 1867 was only /i, 888,000, or 

 something over ^300,000 per annum, at a time when Brazilian 

 diamonds commanded a higher price than at present, and now they 

 produce much less. His statement that the opal is out of fashion 

 would have been true several years ago, but is not to-day, when 

 more of these stones are sold, and at better prices, than ever before. 



The carat is given as 3.174 grains ; whereas, since there are 151.5 

 English diamond carats in an English Troy ounce of 480 grains, an 

 English carat would be 3.1683168 Troy grains, or, less e.xact, 3.168. 

 A diamond carat is always divided into four diamond grains equal- 

 ling .792074 of a Troy grain. If 31.103 grams equal an English 

 Troy ounce, a carat would be .205304 of a gram. 



An international syndicate composed of London, Paris, and 

 Amsterdam jewellers, wishing to establish a uniform carat, in 1877 

 confirmed .205, however, as the true value of a carat, in which case 

 we have 151.76 carats in an ounce Troy. 



These may seem trifling differences, but yet they are enough to 

 affect a $10,000 lot of diamonds, worth $100 a carat, to the amount 

 of $4.83 between the 3.174 carat and the 3.168 carat, and $19.80 

 between the former and the syndicate carat. 



It would perhaps have been better to make the reference to 

 imperial jade, which he mentions several times, under the head 

 of the jade-quarries of Burma, as this {Feitsui) imperial jade is 

 jadeite, not jade, and is generally only emerald green in spots or 

 streaks, the mass being a dead white, lending a vividness to the 

 green which occasionally almost rivals the emerald, and has the 

 hardness of 7. 



Of the articles of jade shown by the New Zealand Court at the 

 colonial exhibition, England, Professor Simmonds says, " Evidencing 

 the skill of the Maoris in working this hard material, the second 

 in this respect to the diamond, although much more fragile," etc. 

 This would lead one to infer that the material possesses great 

 hardness, when, in fact, the hardness of jade is only 6. 5, less even 

 than that of rock crystal, and it can be worked with sand, by which 

 laborious means, undoubtedly, all of the aboriginal ornaments of 

 the Maori were made. So far as its fragility is concerned, it is 

 the toughest of all known minerals, and this is the reason why it is 

 so difficult to v^fork. It would require less time to polish twenty 

 surfaces of agate, which is harder than jade, than it would to polish 

 one of jade on the same wheel. Krantz, the mineral-dealer of 

 Bonn, having a fifty-pound piece of jade which he wished broken 

 into small hand specimens, a friend kindly offered him the use of a 

 large half-ton trip hammer to break it with. At the first blow the 

 hammer was demolished, and the jade was only fractured by being 

 heated and thrown into cold water. 



We frequently hear minerals or gems loosely spoken of as 

 second or third in hardness to the diamond. On the Mohs scale of 

 hardness, the diamond is represented by 10, the sapphire by 9, topaz 

 8, and quartz 7 ; but, although the difference on the scale is only i, 

 there is room for several substances between the diamond and the 

 sapphire ; and, as we have no such known substance in nature, we 

 place diamond on 10. In reality, so great is the difference between 

 these two substances, that, if the hardness of the sapphire is 9, that 

 of the diamond would be fully 100, relatively to the rest of the 

 scale. Professor Simmonds also says that coral has the hardness 



and brilliancy of agate. Quartz and agate are placed at 7 in the 

 Mohs scale, whereas coral has only the hardness of about 3, the 

 same as that of marble (calcite), and can be scratched by fluorite. 

 It is impossible to see how this opaque substance can be said to 

 " shine like a garnet, with the tint of the ruby." 



A word, in closing, about the hardness of agate and rock crystal. 

 Mineralogically these are classed together at 7 ; but in reality the 

 crystalline varieties should be 7, and the crypto-crystalline varieties 

 7.3, since they will readily scratch quartz, and quartz will not 

 scratch them. George F. Kunz. 



New York, Oct. 31. 



Living Lights. 



We have noticed in your journal {Science, x. No. 246) a review 

 of the book on phosphorescence called ' Living Lights.' The 

 writer, it seems, must have made a very hasty perusal to have 

 failed to see that the statements therein are not conjectural, but in 

 each case are from individuals we are accustomed to honor as 

 credible witnesses. 



The fact of this review being in the columns of a science journal 

 is, of course, the only reason for our interest in it. The most chari- 

 table construction which we can put on this surprising exhibition 

 of lack of knowledge is that the reviewer did not notice the array 

 of great names which support the statements of the book, for we 

 cannot think that any one would knowingly dispute the words of 

 such men — and naturalists. 



The reviewer starts off by throwing discredit and ridicule on the 

 entire world of luminosity, seemingly denying that attribute to all 

 living objects. He says, " Not only do fire-flies' fly, glow-worms 

 glow, zoophj'tes twinkle in the sea, but sea-anemones, alcyonarians, 

 gorgonias, star-fishes, earth-worms, crabs, shell-fish, lizards, frogs, 

 toads, fishes, birds, monkeys, and men must be added," etc. 



We confess to embarrassment in approaching the task of replying 

 to such, for one is impressed with the notion that some occult jest 

 is intended ; but again we are reminded of the character of the 

 journal, and a feeling of surprise follows at the incomprehensible 

 lack of knowledge displayed regarding the subject in hand. 



The reviewer continues, " There is no excuse for conjectural 

 illustrations, and ideal views of possible appearances." Shall we 

 inform him that twelve of the plates in ' Living Lights ' are process 

 copies taken from lately published bulletins of M. Filhol, M. Dubois, 

 and from sketches of the deep-water dredged objects obtained by the 

 gentlemen of the' Challenger,' ' Travaileur,' ' Porcupine,' ' Majenta,' 

 and others, several of whom kindly furnished the author with ad- 

 vanced papers for use in his work ? 



Thus for twelve of the illustrations : for the remaining ones, it 

 were absurd indeed to defend them. The former, as being matter 

 not yet widely extant, some of it not published outside of society 

 bulletins, may well be regarded as unfamiliar. The quotation which 

 the reviewer takes from the book is treated so as to mislead. The 

 author evidently meant to convey that it is difficult to represent the 

 phenomenon of luminosity in marine animals, as their integrity is 

 injured on exposure to air, though no question is entertained of 

 their luminosity. A kindly review of this portion would rather 

 praise the caution exhibited by the author in stating that the 

 pictures may possibly not exactly portray the real appearance as it 

 exists in the sea. The statements of the reviewer are so sweeping 

 and (possibly) damaging among those not informed, it would seem 

 advisable to state facts, though it is a humiliating thought that the 

 brilliant work of so many eminent men should in such quarters be 

 unknown. 



It is but justice to do this, as the author of ' Living Lights ' is at 

 present beyond reach, at a distance from home, and of course un- 

 able to reply seasonably. 



The statement, " zoophytes twinkling in the sea " might well 

 have covered the ground for one group, without enumerating "sea- 

 anemones, alcyonarians, gorgonias," etc., also ; but this enumera- 

 tion will serve to suggest what objects concern us, as those arraigned 

 for false attributes. We presume that few will deny the luminous 

 gift to fire-flies, glow-worms, etc., which are mentioned in this 

 connection. Let us, then, pass to the sea-anemone record. Colo- 

 nel Pike of Brooklyn, an American naturalist not to be ques- 

 tioned, has given at length his testimony, and we know that the 

 author himself has an experience as to their luminosity, which. 



