March 12. 1896] 



NATURE 



437 



producing photographic effects always appear to produce strong 

 fluorescent efl^ects on plalino-cyanide of barium, so that the 

 fluorescence of this affords an indication of the photographic 

 efficiency of the radiations emitted from the tube. 



Rali'H R. Lawrence. 

 Massachusetts Institute of Technology, 

 Boston February 26. 



Is it quite correct, as Prof. Lodge puts it, to call the X-rays 

 anodu because they start from a point (surface of glass, or of 

 metal foil, &c.) opposite the kathode? It may be true that a 

 surface upon which the kathodic discharges are l)eing directed 

 acquires thereby some properties common to the anode : but it 

 is not an actual anode. Further, I think that so far there is no 

 proof that these rays start from an anode unless that anode is 

 itself in the line of the kathodic discharge. Hence I submit 

 that anti'kathodic would be a more correct term to use in 

 describing them. They can certainly be made to start from a 

 portion of the kathode itself by shaping it so as to concentrate 

 the kathodic discharges (or " radiant matter"') upon a prolong- 

 ation of itself. 



Whilst dealing with this point, might I mention that a phos- 

 phorescent enamel, made by incorporating calcium sulphide in a 

 very fusible enamel-glass, appears to form an excellent anti- 

 kathodic surface for generating X-rays. 



SlI.VANUS P. Thomi'son. 



Finslniry Technical College, March 9. 



We enclose a print of a " Rontgen" photograph taken by us 

 some time ago, which shows very clearly that it is to the mineral 

 constituents that bone owes its opacity to the " X-rays." Two 

 human finger-bones were obtained as nearly alike as possible. 

 One was decalcified by treatment with dilute hydrochloric acid 

 for some days, the other being soaked in water for the same 

 period. The calcium phosphate, carbonate, &c., dissolved by 

 the hydrochloric acid, were precipitated by ammonia and am- 

 monium carbonate, and the precipitate, after washing, was 

 spread on paper, so as to cover an area about equal to that 

 which would be covered by the original bone. . This precipitate, 

 together with the bone which had merely been soaked in water, 

 and the "decalcified" bone (which had shrunk during treatment 

 with the acid), were then placed upon a photographic plate and 

 exposed in a cardboard box to the radiations from a Crookes' 

 tube excited by a small " Tesla" apparatus. 



The picture thus obtained, shows clearly that while the de- 

 calcified bone is almost without action on the "X-rays," the 

 mineral matter is practically as opaque as the bone before 

 treatment with acid. 



The print shows, however, that both the original bone and the 

 calcium phosphate are only relatively opaque, but that they do 

 allow some "rays" to pass, for the photograph shows half-tones, 

 and not merely an outline. J. D. Cormack. 



Herbert Lngle, 



The Yorkshire College, Leeds, March 4. 



Remembering that scientific men are pledged, beyond all 

 others, to accuracy and observance of rule, I am emboldened to 

 protest against the use of two words which are sometimes 

 employed to describe the pictures produced through the agency 

 of Rontgen's rays. I mean " shadowgram" and " radiogram." 



Both of these offend against a primary rule for the formation 

 of new compound words, which requires that all of the com- 

 ponent parts of any word shall be derived from one and the 

 same language. 



If a word be desired which shall signify a picture produced by 

 rays, let us go to the Greek language only, and form the word 

 " actinogram " ; or to the Latin language only, and form the 

 word ' ' radioscript " ; or else let us be content with some purely 

 I'.nglish compound, such as " ray sketch." G. H. P. 



reappearing in thin streaks and irregular patches of yellowish 

 light in various parts of the sky between north and west. 



At 10 30, it was round in the north. At one time, six well- 

 distanced streaks were counted. They seemed to converge 

 slightly towards the zenith. The light was mainly yellowish, 

 but tinged here and there with pulsating reddish rays. The 

 flickering, or fluctuation in colour and brightness, was distinctly 

 noticeable. 



The phenomenon was not observed after 11.30. 



As auron\; are essentially electrical in character, having some 

 analogies with the brush discharge, it would be interesting to 

 know whether, like the brush discharge from induction coils and 

 influence machines, shcuimv^i.'rap/is might be taken by means of 

 these weird rays. Opportunities for testing their photograjihic 

 qualities occur very frequently in higher latitudes than ours, and 

 even nightly in circumpolar regions, the home of this interesting 

 phenomenon. M. F. O'Reilly. 



De La Salle Training College, Waterford, March 5. 



The Aurora at Waterford. 



Ai lEK a boisterous day and a barometer that went down to 

 28S5, we were favoured last (Wednesday) night with an auroral 

 display. It was first seen here at 8 o'clock, when it appeared in 

 a cloudless, starlit sky as a sheaf of light springing from the 

 western point of the horizon, and stretching along an arc of 

 30° up towards the FMeiades. 



Its colour, at first silvery white, gradually faded away. 



An Unusual Meteor. 

 At 8. 3 1 on Sunday evening, March i, when half a mile north ot 

 York Minster, I caught sight of a meteor slowly falling vertically 

 almost due east. It was then passing over the two small stars 

 V and I \]vsx Majoris, which at the time were at an altitude of 

 43'', azimuth 5" north of east. Seeing that it meant to last 

 awhile, I proceeded to repeat the alphabet in the orthodox 

 manner (once through, each letter quickly l)ut distinctly 

 enunciated, requiring 4 seconds). Having gone over it twice, I 

 must confess that my amazement at the meteor's duration made 

 me pause. But it kept on, so I continued, getting through it 

 twice more. Then, after a second involuntary but very un- 

 scientific pause, I finished the alphabet a fifth time before the 

 phenomenon came to a close. In all, I must have watched it at 

 least 25 seconds. After some 10 seconds, when about the same 

 j altitude as )3 Leonis (24"), a smaller meteor (fourth magnitude) 

 i appeared 1° to the left, at an angle of about 40°, and, proceed- 

 j ing at the same speed of under 2" per second, lasted 3 or 4 

 seconds. The original, of which this was doubtless a fragment, 

 was between first and second magnitude, but with a distinct 

 ! disc, and was followed by a train of sparks, reddish like itself, 

 ' which was never more than 2° or 3 long, or lasting only i 

 i or 2 seconds. The fragment had also a slight train. The main 

 I mass seemed to pause slightly about this spot, perhaps because 

 of this explosion. From the first it moved slower and slower, 

 doubtless an effect of perspective, and finally disappeared almost 

 due east (within 5° north of east), only 5° or so above the 

 horizon, in the unusually clear sky just above the rising moon. 



Whilst making notes, a gentleman came by, who said that he 

 had seen it earlier, when as high as, and very near t and ^ 

 Ursit Majoris (the hind paw), or about an altitude of 58°, 5" 

 north of east. Thus its angular path was 53". As the additional 

 distance was nearly half that observed by myself, it must have 

 been visible for at least 7 seconds before I saw it, or 32 

 seconds in all. This makes due allowance for its apparently 

 quicker motion at first. But the gentleman himself thought 

 that he had not seen the actual commencement. 



It is to be hoped that some other reports will be received, for 

 its path must have been of extraordinary length, even if it was 

 only travelling at ten miles per second, which is the almost 

 irreducible minimum for a meteor. 



A third observer saw it from indoors, appearing from above 

 the window and falling vertically down the panes. It is a 

 reasonable assumption, for a meteor of so great duration, that it 

 first appeared at a height of 100 miles and reached within 30 

 miles of the earth. If so, its approximate path would be from 

 above 25 miles otT Bridlington to the coast of Denmark, north- 

 east of Heligoland. The flight would be 360 miles, or rather 

 ] over 10 miles per second. 



Bootham, York. J. Edmund Clark. 



RECENT WORK OF THE GEOLOGICAL 



SURVEY OF THE UNITED STATES. 



L 



OWING to the fact that much of the sphere of opera- 

 tions of this Survey lies in a new country, it is 

 compelled to undertake a great deal of work of a class 

 which does not usually fall to the lot of a body of 

 geologists ; chief amongst this stands topograp hical 



NO. 1376, VOL. 53] 



