274 



NATURE 



[January 23, 1896 



VOTE OF CONVOCATION ON THE COWPER 



COMMISSION SCHEME. 

 A NOTHER step has been taken in the long contro- 

 -^~*- versy with respect to the equipment of the Univer- 

 sity of London with teaching functions. While the other 

 bodies represented on the recent deputation to the Duke 

 of Devonshire had passed resolutions asking the Govern- 

 ment to introduce a Bill similar to Lord Playfair's 

 "London University Commission Bill, 1895," but with 

 an added clause giving a right of appeal to the Privy 

 Council (Nature, December 5, 1895), Convocation had 

 not expressed any opinion either on the Bill or on the 

 proposed appeal, owing to Lord Playfair's Bill being 

 introduced into the House of Lords too late to allow of 

 a resolution approving its terms to be moved at the last 

 meeting in May. On Tuesday last, the Annual Com- 

 mittee recommended Convocation to adopt the following 

 resolution: "That this House desires the early intro- 

 duction into Parliament of a Bill for the reconstitution 

 of the University similar to that introduced last 

 year by Lord Playfair, but with an inserted clause 

 securing to the Senate, to Convocation, and to other 

 bodies affected, the right of appeal to the Privy 

 Council on any of the provisions which may here- 

 after be settled by the Statutory Commission." This 

 resolution was carried by 470 votes against 244, and thus 

 for the third time Convocation, in the only legal way, has 

 pronounced decisively in favour of the Cowper Commis- 

 sion scheme. The progressive rise in the majorities is 

 not the least satisfactory feature of the struggle in Con- 

 vocation — a majority of 24 in a house of 290 in January 

 of last year rose to 122 in a house of 354 in May, and 

 has now become 226 in a house of 714. The next step 

 rests with the Government, but in view of the remarkable 

 unanimity existing among the bodies affected by the 

 schem.e, and the universally favourable attitude of the 

 metropolitan press towards it, we can be in no doubt as 

 to what the final settlement must be. 



ON A NEW KIND OF RAYS} 

 (0 A I^ISCHARGE from a large induction coil is passed 

 -'^^ through a Hittorfs vacuum tube, or through a 

 well-exhausted Crookes' or Lenard's tube. The tube is 

 surrounded by a fairly close-fitting shield of black paper ; 

 It IS then possible to see, in a completely darkened room,' 

 that paper covered on one side with barium platino- 

 cyanide lights up with brilliant fluorescence when brought 

 into the neighbourhood of the tube, whether the painted 

 side or the other be turned towards the tube. The 

 fluorescence is still visible at two metres distance. It 

 is easy to show that the origin of the fluorescence lies 

 within the vacuum tube. 



(2) It is seen, therefore, that some agent is capable 

 of penetrating black cardboard which is quite opaque 

 to ultra-violet light, sunlight, or arc-light. It is there- 

 fore of interest to investigate how far other bodies can 

 be penetrated by the same agent. It is readily shown 

 that all bodies possess this same transparency, but in 

 very varying degrees. For example, paper is very trans- 

 parent ; the fluorescent screen will light up when placed 

 behind a book of a thousand pages ; printer's ink 

 offers no marked resistance. Similarly the fluorescence 

 shows behind two packs of cards ; a single card does 

 not visibly diminish the brilliancy of the light. So, again 

 a single thickness of tinfoil hardly casts a shadow' on the 

 screen ; several have to be superposed to produce a 

 marked effect. Thick blocks of wood are still trans- 

 parent. Boards of pine two or three centimetres thick 

 absorb only very little. A piece of sheet aluminium, 15 

 mm. thick, still allowed the X-rays (as I will call the rays, 



1 By W. C Rontgen. Translated by Arthur Stanton f.oi 

 benchteder IVurzburger Physik-medic. GeselUchaft, 1895, 



NO. 1369, VOL. ^l\ 



for the sake of brevity) to pass, but greatly reduced the 

 fluorescence. Glass plates of similar thickness behave 

 similarly ; lead glass is, however, much more opaque 

 than glass free from lead. Ebonite several centimetres 

 thick is transparent. If the hand be held before the 

 fluorescent screen, the shadow shows the bones darkly, 

 with only faint outlines of the surrounding tissues. 



Water and several other fluids are very transparent. 

 Hydrogen is not markedly more permeable than air. 

 Plates of copper, silver, lead, gold, and platinum also 

 allow the rays to pass, but only when the metal is thin. 

 Platinum '2 mm. thick allows some rays to pass ; silver 

 and copper are more transparent. Lead 1-5 mm. thick 

 is practically opaque. If a square rod of wood 20 mm. 

 in the side be painted on one face with white lead, it 

 casts little shadow when it is so turned that the painted 

 face is parallel to the X-rays, but a strong shadow if 

 the rays have to pass through the painted side. The 

 salts of the metals, either solid or in solution, behave 

 generally as the metals themselves. 



(3) The preceding experiments lead to the conclusion 

 that the density of the bodies is the property whose 

 variation mainly affects their permeability. At least no 

 other property seems so marked in this connection. But 

 that the density alone does not determine the trans- 

 parency is shown by an experiment wherein plates of 

 similar thickness of Iceland spar, glass, aluminium, and 

 quartz were employed as screens. Then the Iceland 

 spar showed itself much less transparent than the other 

 bodies, though of approximately the same density. I 

 have not remarked any strong fluorescence of Iceland 

 spar compared with glass (see below. No. 4). 



(4) Increasing thickness increases the hindrance 

 offered to the rays by all bodies. A picture has been 

 impressed on a photographic plate of a number of super- 

 posed layers of tinfoil, like steps, presenting thus a 

 regularly increasing thickness. This is to be submitted 

 to photometric processes when a suitable instrument is 

 available. 



(5) Pieces of platinum, lead, zinc, and aluminium foil 

 were so arranged as to produce the same weakening of 

 the effect. The annexed table shows the relative thick- 

 ness and density of the equivalent sheets of metal. 



Platinum 



Lead 



Zinc 



Aluminium. 



Thickness. Relative thickness. 

 •QiS mm. ... I 



■050 „ ... 3 ... 

 6 ... 



•100 

 3-500 



200 



Density 

 21-5 

 1 1 -3 



7-1 



2-6 



the Sitzitngs- 



From these values it is clear that in no case can we 

 obtain the transparency of a body from the product of its 

 density and thickness. The transparency increases much 

 more rapidly than the product decreases. 



(6) The fluorescence of barium platinocyanide is not 

 the only noticeable action of the X-rays. It is to be 

 observed that other bodies exhibit fluorescence, e.g. cal- 

 cium sulphide, uranium glass, Iceland spar, rock-salt, &c. 



Of special interest in this connection is the fact that 

 photographic dry plates are sensitive to the X-rays. It 

 is thus possible to exhibit the phenomena so as to 

 exclude the danger of error. I have thus confirmed 

 many observations originally made by eye observation 

 with the fluorescent screen. Here the power of the 

 X-rays to pass through wood or cardboard becomes 

 useful. The photographic plate can be exposed to the 

 action without removal of the shutter of the dark slide 

 or other protecting case, so that the experiment need not 

 be conducted in darkness. Manifestly, unexposed plates 

 must not be left in their box near the vacuum tube. 



It seems now questionable whether the impression on 

 the plate is a direct effect of the X-rays, or a secondary 

 result induced by the fluorescence of the material of the 

 plate. Films can receive the impression as well as 

 ordinary dry plates. 



