November, 1913. 



KNOWLEDGE. 



409 



white solar light that the monochromatic light of 

 the hydrogen flame may be seen when there is no 

 eclipse. By making an extremely long spectrum 

 the ordinary sunlight is so spread out as to be in- 

 significant, whilst the red monochromatic light of the 

 flames retains its intensity, and thus we are enabled 

 to see these red flames during ordinary sunlight. 



THE PHOTOGRAPHIC FILM. 

 Another principle adds greatly both to the power 

 of the ordinary telescope and particularly when the 

 optic tube is armed with a prism. It is the 

 application of photography to astronomy. One 

 wonderful effect is obtained by photography ; the 

 human eye soon tires, whereas the photographic 

 film will continue to add to its effects for hours or 

 even days, and thus filmy masses of light that 

 would for ever have remained undetected imprint 

 their message on the sensitive plate until, as in the 

 case of the nebulae of the Pleiades, details of 

 structure are shown connecting up the whole of 

 this beautiful cluster of stars, yet with the ordinary 

 telescope, used by the naked eye, the stars seem to 

 stand out on an almost absolutely dark background. 

 An example still more remarkable of the minuteness 

 of its detail is given in Figure 421. Another 

 effect of photography is that the film may be 

 left exposed, or exposed automatically, so as to 

 record effects when no one is near. Perhaps the 

 most wonderful of all the applications of photo- 

 spectroscopy is the work done in Harvard Observa- 

 tory and its branches, of the wholesale automatic 

 photography of the spectrograms of large numbers 

 of stars, taken all at once. 



THE IMPORTANCE OF THEORY. 



Years ago Newcomb feared that the science of 

 astronomy would be buried beneath the tremendous 



mass of uncorrelated facts that were then accumu- 

 lated ; yet in spite of this the whole endeavour of 

 astronomy, until quite recently, has been merely 

 further accumulations. This state of things is 

 passing ; endeavours to correlate astronomical 

 phenomena are being made by able men, both in the 

 New World and the Old. And although these 

 endeavours have not hitherto been eminently 

 successful, nor much accepted save by their respect- 

 ive propounders, yet the attempts are promising 

 symptoms of the times. There is a distinct advance 

 on the part of astronomers in their willingness to 

 receive the assistance of workers in other branches 

 of science. Physicists and chemists are allowed to 

 read papers before astronomical societies. On the 

 other hand the learned societies representing 

 experimental science now make room for cosmic 

 generalisations. At the British Association Meeting 

 joint conferences of many sections were held. 



All this is very hopeful, for nothing causes science 

 to spring forward by such leaps and bounds as great 

 generalisations. Although they are thus the mile- 

 stones in human progress, generalisations have 

 generally been neglected for something like half a 

 century. We are not without examples of disastrous 

 neglect in the present age of science. The broaden- 

 ing outlook gives us at present a better prospect and 

 supplies a probability that research will be no 

 longer mere vicious specialisation, but each expert 

 will do his work with definite purpose and in 

 correlation with the sum of knowledge. 



Amid all the tremendous rush of present discovery 

 there is no branch of knowledge that is correlated so 

 widely in all directions as spectroscopy, and no 

 scientific worker should be ignorant of its basic 

 principles. 



CORRESPONDENCE. 



RAY FLORETS IN THE DISC OF 



CHR YSA N THEM UM. 



To the Editors of " Knowledge." 



Sirs, — I enclose you a photograph of a specimen of the 

 common Marguerite (see Figure 505, page 431) in which two 

 strap florets have been produced in the centre of the group 

 of tubular ones ; the two strap florets were surrounded at 

 their bases by a small involucre. I have not seen a flower 

 like this before, and thought the reproduction of the photo- 

 graph might be of interest to readers of " Knowledge." 



Newcastle-on-Tyne. JOHN HUME. 



AUSTRALITES. 

 To the Editors of " Knowledge." 



Sirs, — The short account given by Mr. G. W. Tyrrell 

 (page 308) on the subject of " Australites " (which formed the 

 subject of a memoir by Mr. E. J. Dunn, of Victoria, 

 Australia) has interested me very much. 



In the year 1909 it fell to my lot to make a journey from 

 the coast of Vera Cruz up to near Mexico City on horseback, 

 accompanied by another geologist. The trip took four days, 

 and we rose close on seven thousand feet. 



On the second day out, my companion who had done the 



same journey previously, said to me, " To-morrow we shall 

 pass beds of sand and sheets of basalt, and I want you to 

 give me your unbiased opinion about the relative geological 

 positions of the sands and basalt, i.e., whether the sands lie 

 above the basalts or vice versa." 



The third day brought us to the sands, and on seeing a 

 pure white silvery sand I at once said, " Why, that is not 

 sand, it is volcanic ash," and you can imagine my astonish- 

 ment when, on examining the sand with my pocket lens, I 

 found that a large percentage of the grains consisted of 

 perfect little bubbles. 



No doubt the greater part of the remaining grains would 

 be " Australites," but this I did not know at the time. 



I think that the conditions in Mexico prove conclusively 

 volcanic origin, for amongst the sand were later on discovered 

 pieces of fibrous pumice and a large amount of dark green 

 obsidian. 



The obsidian, by the way, gave the source from which the 

 supply was obtained to make the numerous arrow-heads and 

 long flat needle-shaped spears frequently picked up in the 

 coastal regions. 



I hope that the above will prove of interest to your 

 renders 



F. W. MOON (A.M.I.C.E., F.G.S.), 



Tandjong Poera, Sumatra. 



