Aprils, 1877] 



NATURE 



489 



To this amount, however, must be added the portions of the 

 Cape Breton and Inverness Coal Fields lying under the sea^ 

 which, supposing the seams can be worked a distance of five 

 miles beyond high-water mark, will make the total area of the 

 Nova Scotia Coal Fields 859 instead of 18,000 square miles. 



The production in 1874 hss also been greatly overstated in 

 Dr. Si emens' Table, as I find by reference to the Government 

 Inspector's Report for the year 1876, that the production in 1874 

 was only 749,127 tons. R. B. 



[Dr. Siemens informs us that the difference referred to by our 

 correspondent chiefly arises from the fact that in American re- 

 ports Nova Scotia is made to include the maritime province of 

 New Brunswick as well as Cape Breton Island, both of which 

 contain large areas of coal-fields, although those fields are as yet 

 very imperfectly developed. The figures given in the address 

 were taken from Macfarlane's very elaborate work on the ' ' Coal - 

 Regions of America." "With reference to the coal production, 

 this should be for the year 1873, and is also given on the 

 authority of Macfarlane, who quotes from the Report of the 

 Department of Mines. — Ed.] 



Greenwich as a Meteorological Observatory 



A CAREFUL examination of the interesting communication by 

 Mr. Alexander Buchan to the Scottish Meteorological Society, 

 on •' The Temperature of the British Islands," based on observa- 

 tions for the thirteen years ending 1869, fails to support his con- 

 clusion (Naturk, vol. XV., p. 450) that the proximity of London 

 does not appreciably influence the temperature as recorded at 

 the Royal Observatory, and that the temperature of Greenwich 

 during recent years has not been in excess of that of surrounding 

 districts. The evidence is quite the reverse. Extracting the 

 figures, given by Mr. Buchan in the paper referred to, for all 

 the stations within a radius of sixty miles of the metropolis, 

 sixteen in number besides Greenwich, it appears that their mean 

 is SO°"i, that of Greenwich being 50*^ "d. Allowing for elevation, 

 the values are respectively 50° '68 and 51° '13. Omitting, how- 

 ever, several stations such as Camden Town, which, forming 

 part of London, is clearly inadmissible for the comparison, and 

 Maidstone and Canterbury, where observations were made on 

 two years only of the thirteen, the temperature of the ten re- 

 maining stations is 50° '59. Thus, according to data furnished 

 by Mr. Buchan himself, Greenwich is warmer than the south- 

 east of England generally by more than half a degree (o°'54). 

 It may be added that, from the same data, the temperature of 

 the district under consideration north of the Thames is 50° "5, 

 and south of the river 5o°'8. H. S. Eaton 



Centralisation of Spectroscopy 



In his letter (Nature, vol. xv. p. 449) Prof. Smyth makes a 

 statement respecting the new "half-prism" spectroscope which I 

 cannot help thinking must be founded on a misapprehension of the 

 principle involved. This will, I trust, be made clear when my 

 paper is published in the forthcoming number of the Proceedings 

 of the Royal Society ; but meanwhile, as Prof. Smyth appears 

 disinclined to wait for a full explanation of the instrument, I 

 shall be most happy to answer his objections when he informs 

 me what particular " laws of Sir Isaac Newton and nature " are 

 in opposition to the principle of this spectroscope. 



Against Prof. Smyth's confident assertion that all definition is 

 lost in this instrument, which he has never seen and of which he 

 can only know by hearsay, I have only to set the statement that a 

 small experimental spectroscope on the new plan, with two 

 " half-prisms," is, as a matter of fact, decidedly superior in defi- 

 nition, as well as in brightness of spectrum, to the large Green- 

 wich spectroscope, with ten large compound prisms, of which 

 the excellence is sufficiently attested by the accordance of the 

 results obtained for the sun's rotation by its means. This state- 

 ment is based on a careful comparison of the sodium lines, and 

 also of the b group in the solar spectrum, as seen with the two 

 instruments, b^ and b^ with the finer lines in their neighbourhood 

 being shown with remarkable distinctness in the new form of 

 spectroscope, small though it is. In this assertion, I think, I 

 shall be fully borne out by several astronomers to whom I have 

 shown the action of the new spectroscope. 



Though I am not in any way concerned with Prof. Smyth's 

 argument in the earlier part of his letter, I may mention for his 



information that " during the last twenty years " only tujo 

 spectroscopes have been made for Greenwich Observatory (one 

 of these having only a single prism of small dispersion), and that 

 our second or powerful spectroscope was only made three years 

 ago ; whilst the Edinburgh observatory has, for the past Jour 

 years, possessed three spectroscopes which are almost precisely 

 identical with those used with such effect by Dr. Iluggins. 



W. H. M. Christie 

 Royal Observatory, Greenwich, March 27 



Morphology of " Selaginella " 



Bkfore instituting a comparison it is generally prudent to 

 ascertain that the things to be compared are comparable. I am 

 afraid Mr. Comber, who has done me the honour of making 

 some remarks on what I have said in tlie pages of Nature on 

 the primordial type of flowers, has neglected this precaution. 

 If I understand him rightly, he suggests that the " spike " of 

 Selagindla is the homologue of the spike of Carex pulicaris. 

 lie compares, then, the scales bearing macrosporangia of the 

 former with the lower glumes bearing each an ovary of the 

 latter. 



Now in the first place, if he had studied the matter a little 

 more (if he will allow me to say so), he would have seen that 

 the ovule, and not the ovary, is the equivalent of the macro- 

 sporangium, and that the embryo sac, and not the ovule, is the 

 equivalent of a macrospore. This leaves the ovary unaccounted 

 for, and the homology hopelessly breaks down on that point. 



But this is not all. Mr. Comber has omitted all notice of the 

 singular structure, the perigynium, and also of the equally singu- 

 lar structure, the " seta," which it contains along with the ovary, 

 and which happens to be particularly well represented in Carex 

 pulicaris. If he will take the trouble to look at a short paper 

 which I have published in the Journal of the Linnean Society 

 (Botany) vol. xiv., pp. 154-156, pi. xii., he will find that I have 

 carefully discussed the morphology of the female flower of this 

 very plant. I think I have succeeded in showing that far from 

 being a simple racemose inflorescence it is a compound raceme or 

 panicle reduced in a very peculiar manner. I am afraid, there- 

 fore, that Mr. Comber has been led away by resemblances of a 

 very superficial character, and that the fact Selaginella has a 

 "spike" and that Carex has a "spike," is a point of contact 

 between the two about as significant as the existence of a river in 

 both Macedon and Monmouth. 



In fact, far from being plants of a primitive type, the Cype- 

 racecE are generally regarded as reduced representatives of plants 

 of much more fully developed character, the exact nature and 

 relationship of which we have no materials for at present esti- 

 mating. W. T. Thiselton Dyer 



Tungstate of Soda 



With regard to your note (Nature, vol. xv. p. 460) upon 

 muslin rendered uninflammable by tungstate of soda, will you allow 

 me to say that when properly prepared the muslin is fairly unin- 

 flammable. I say uninflammable — not fireproof. There can be no 

 doubt from experiments made in Prof. Gladstone's laboratory that 

 muslin, prepared with a sufficient quantity of the salt will not 

 catch fire by ordinary means, but no one could reasonably expect 

 it to stand an auto daje such as that to which I saw Dr. Wright 

 subject his dummy, and fortunately not his assistant, last Saturday 

 fortnight. Matthew W. Williams 



Chemical Laboratory, Royal Institution 



Traquair's Monograph on British Carboniferous Ganoids 



Will you kindly permit me through the medium of your 

 journal, to correct and apologise for a- very awkward blunder 

 which occurs in the first part of my monograph on British car- 

 boniferous ganoids, recently published by the Palseontographical 

 Society ? In the introduction I have advocated the retention of 

 the Dipnoi as a distinct order of fishes, but at page 41, in a 

 manner unaccountable to myself, for I certainly did not mean it, 

 I have included them as a sub-order of the Ganoidei. That this 

 " slip of the pen " was not detected in the revision of the proofs 

 must have been due to an amount of carelessness of which I am 

 justly ashamed. R. H. Traquair 



Edinburgh, April 2 



