338 



NATURE 



\_A71gust 12, 1880 



kaoliiiisation of the felspar in each ton of rock would require to 

 elevate it to an extent it would be difficult to estimate. 



To this Mr. Cliurcli, who derives -his heat from the hydration 

 of silicate of aluminium during the formation of kaolin, objects 

 that the whole of the alkalies liberated by the decomposition of 

 felspar do not become dissolved in water, and that their amount 

 cannot cun^equcntly be taken as a measure of the quantities of 

 that mineral which have been decomposed. 



In support of this argument he states that clays from tlie 

 immediate neighbourhood of the Comstock lode still contain 

 above a\ per cent, of alkalies, and ignores the fact that the linal 

 result of' kaolinisation is the production of a hydrated sUicate of 

 aluminium free from alkalies. The clays in question mu.,t 

 consequently be regarded as containing undecomposed felspar 

 which cannot have contributed to any increase of temperature. 



Admitting however for the sake of argument that all the 

 felspar has been decomposed, and that three-fourths of the 

 alkalies present have been retained by the resulting clay, the 

 heat corresponding to the decomposition and hydration of the 

 felspars in a ton of rock must be reduced by tliree-fourtbs. If, 

 therefore, as before, to simplify our ideas, we regard the heat 

 required to produce the observed effects as due to a single 

 variation of temperature, the original temperature must have 

 been above twenty times higher than the melting point of gold, 

 which appears as improbable as that found on the assumption 

 of the whole of the alkalies entering into solution. 



The assumption now made, namely, that much of the kaolini- 

 sation of the felspar is accomplished by aqueous vapour which is 

 entirely absorbed by the rock, and which does not give rise to 

 any aqueous solutions, involves conditions of which we have no 

 known example, and of which it is difficult to conceive the 

 existence at such great depths below the water-level of the 

 country. 



This view of the question was not advanced by Mr. Church in 

 his original paper of 1S7S, and has probably occurred to him 

 subsequently to the publication of my observations in the 

 Quarterly Journal of the Geological Society in the following year. 

 If however the possibility of such an alteration were admitted, it 

 certainly could not be ascribed to kaolinisation, since the removal 

 of the alkalies in felspars is an essential factor in that trans- 

 formation. 



With regard to the hot spring which formerly issued from 

 between slate rocks and an elvan dyke at Wheal Clifford Mine 

 in Cornwall containing notable quantities of chloride of lithium 

 and other alkaline salts, cited by Mr. Church in his recent 

 pamphlet in support of his views with respect to kaolinisation, 

 the effect has probably been taken for the cause. Hot water is 

 known to be a better solvent of mineral matter than cold water, 

 and it has been shown by Daubree that at high temperatures 

 and under great pressure it is even capable of rapidly dissolving 

 silica out of glass, and of leaving it in the form of crystallised 

 quartz. 



We have no direct evidence that the dissociation of the 

 constituents of felspar and the subsequent hydration of the 

 clay produced give rise to any liberation of heat. It is well 

 known that the temperature of mines situated in granite, where 

 kaolinisation is constantly going on, is lower than that of those 

 worked in clay-slate, while high temperatures or thermal springs 

 are not more frequently observed in masses of kaolinised granite 

 than elsewhere. 



The mines on the Comstock lode are situated in a highly- 

 volcanic region of very late tertiary age, and in the almost 

 immediate vicinity of lava-flows and boiling springs. Until, 

 therefore, stronger evidence than that yet furnished shall have 

 been brought forward, it is probable that the majority of geolo- 

 gists may continue to ascribe these phenomena to the action of 

 volcanic agencies. J. Arthur Philufs 



18, Fopstone Road, Kensington, S.W., August 9 



British Museum Attendants 

 As you are a free lance in British Mu-eum matters, will you 

 not make some remarks on the attendants ? They are, as a 

 body, intelligent and desirous of learning, but no attempts seem 

 ever to be made to instruct them in the subjects of their dejiart- 

 ments ; and all the information they possess is picked up by 

 scraps, from overhearing the remarks of their chiefs to distin- 

 guished visitors. 



Many of them do what they can to teach themselves ; but why 

 should they not have some regular training, and be competent to 

 give simple and informal description-lectures to parties who 



really go for instruction ? It cannot be said that it would imperil 

 their charges by occupying their attention, when we see how 

 a far scantier supply of care-takers completely;- guard South 

 Kensington. ,.v 



The object is not to get a higher paid and superior class of 

 men, but to give them the advantages they might reasonably 

 enjoy, and use them as rational beings. I have heard some of 

 them deplore the way in which they are treated, " like so many 

 watch-dogs " ; the snuff-taking to keep awake ; the lapses of the 

 stouter ones into afternoon naps ; the forbidden conversations, 

 even on the objects of their care, with visitors ; the reading of 

 all the advertisements of the Times, for lack of better interest ; 

 all these are familiar subjects, as you will find if you once tap 

 the flow of forbidden talk successfully. 



Some attention to them might prevent such a colloquy as I 

 once had with a flashy-looking fellow on one of the many un- 

 labelled objects in his department, I asked, "Do you know 

 where that squared block is from that stands on that terminal 

 ornament ? " Gallio (w ith a flower in his button-hole) : " Which 

 do you mean?" "That one which has another rough block 

 standing on it." Gallio (impatiently) : " Well ! what about 

 it?" "Do you know where it came from?" Gallio (with 

 ineffable contempt): "No! indeed; I don't know where it's 

 from. I don't know anything about it. " If you should care to 

 quote this, I can vouch for its accuracy, as I noted it at the time. 



Bromley, Kent Wm. Flinders Petrie 



Quassia and Mosquitos 



In Nature, vol. xxii. p. 11, I read a letter in which the 

 employment of a \\ash made from a decoction of quassia wood 

 was recommended as a protection from the attacks of mosquitos 

 and other insect pests. After reading the above-named letter I 

 sent some of the quassia to my son, who is a surveyor camping 

 out on the prairie in Dakotah Territory, U.S.A., in a part much 

 infested in hot weather by mosquitos. In a recent letter my 

 son states that he has repeatedly tried the wash with quassia, but 

 without any beneficial results, the mojquitoj having attacked 

 him even before the solution had dried on his skin. 



I have suggested that he should try carbolic acid ointment, if 

 he can procure any, as English insects do not like the carbolic 

 odour. 



Possibly the mosquitos referred to in your correspondent's 

 letter may have been much better fed than the North American 

 tormentors. 



If any of your numerous readers could communicate some 

 effectual protection against the attacks of these pests, it would 

 be a great boon to those who suffer so much from them. 



Manchester, August 9 J. B. Dancer 



Fascination 



A VERY simple explanation may be offered of the seemingly 

 mysterious facts of fascination, whether in man or the lower 

 animals. Every one knows the old and ludicrous problem 

 requiring us to decide what would happen to a hungry donkey 

 placed at a spot exactly equidistant from two quite equally 

 attractive bundles of hay. In theory the creature starves, being 

 unable to make up its mind to choose one bundle rather than the 

 other without any reason for such choice. In practice it is 

 generally supposed that the unsteadiness of this world's affairs 

 would speedily destroy the equilibrium of motives and leave the 

 donkey free to make its meal of one or other of the bundles. 

 But in critical emergencies-, such as those mentioned in Mr. 

 Curran's letter, when shot and shell are flying rapidly towards 

 their victims, almost instantaneous decision is necessary. The 

 circumstances are such that movement either to the right or to 

 the left would be equally salutary and efiicacious, but for the 

 very reason that one movement would be just as good as the 

 other, the mind makes its fatal pause of indecision. A man 

 standing in the path of an advancing express train, and a small 

 biid eyed by a snake, are probably affected both in the same 

 manner. There need be no nrrr.li i'fluence in the eye of the 

 basilisk, as there can be no magical power in the iron and brass 

 of the steam-engine, to transfix and fascinate the prey. Terror 

 may no doubt in some instances paralyse theljrain and make it 

 incapable of choosing the method of escape, which to an intellect 

 unembarrassed and free from panic would be the one obviously 

 worthy of choice, but in the military examples cited by Mr. 

 Curran it would be indecent to suggest such anexjilanation of 

 the facts, and needless when the simpler solution is available. 



Tunbridge Wells, August 9 Thomas R. R. Stebbing 



