44 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Mar., 1904. 



After the transferrins the low layers of the original paper 

 will in the new paper be uppermost. The warm water will, 

 therefore, be able to rinse off any jelly layers which have 

 not become insoluble by the effect of light. On the portions 

 corresponding to the sky, the green and red layers which are 

 not struck by light will be removed, the blue layer only 

 remaining. In the red wall, where the light as above shown 

 has penetrated all the existing layers down to the lowest red 

 layer, which, after the transferring is above all the remaining, 

 no alteration will be produced, while in the portions corre- 

 sponding to the green leaves only the red layer, which 

 now covers the green colour, will be washed off by 

 the water, when the green colour becomes visible, covering 

 the blue layer lying underneath. In practice, it has been 

 found advisable to use a larger number of coloured 

 layers instead of those corresponding to the three funda- 

 mental colours only, so as to produce all the shades required ; 

 up to 14 pigments are thus used. The abo\e process has 

 been developed in the laboratory of Dr. Ad. Hesekiel 

 and Co., Berlin. .As a matter of course, any old negati\-es 

 taken at any time may be made to reproduce the true colours 

 of the original. — A. G. 



The Blondlot or N-Rays 



In view of the interest which has been imparted to M. Blond- 

 lot's X-rays by the investigations of Professor Charpentier, 

 and also by the doubts which ha\e been thrown on the real 

 existence of the rays, we have thought that it might be inter- 

 esting to collect the ascertained facts and observations con- 

 cerning these rays. For this summary we are chiefly indebted 

 to a series of articles contributed 'by Mons. La\ erune to 

 Casinos. 



The X-rays were discovered bv M. Blondlot, of Xancv. 

 while studying Rontgen rays. By endeavouring to pass rays 

 through a sheet of aluminium, he separated quite a new group 

 of radiations. The rays he found were such as to penetrate 

 alumunum. black paper, or wood. They could be polarised 

 and might be deflected or diffused, but they produced neither 

 fluorescence nor photographic action. They were invisible, 

 gave no sensation of light, but augmented the brilliancy of an 

 electric spark. 



It is this property which enables us to detect the ravs. They 

 are incapable of exciting phosphorescence in bodies which caii 

 ac(imre this property from the action of light ; but when such 

 a body, sulphuret of calcium for instance, has first been ren- 

 dered phosphorescent by exposure to light, then if submitted 

 to the action of these rays, especially if they are focussed bv 

 a quartz lens, one can see the brightness of the phosphor- 

 escense perceptibly increase. In the same way if one directs 

 them on to a little flame of gas at the end of a metal tube 

 pierced by a very minute orifice this flame, entirely blue, 

 becomes whiter and more luminous. We are now furnished 

 with these means of detecting the presence of these radiations. 

 M. Blondlot, struck with certain analogies that they present 

 with the radiations discovered by Professor Rubens in the 

 emissions of the Auer Burner, asked himself if the X-rays 

 were not identical. An Auer burner .was enclosed in a kind 

 ot Lantern of sheet iron closed at all points, with the exception 

 ol the openings for the escape of air and the gas from com- 

 bustion, and so arranged as to prevent the passage of any 

 light. A rectangular window opened in the iron at the light of 

 the incandescent mantle was closed bv an aluminium sheet 

 I mm. in thickness. The chimney of" the Auer burner is of 

 sheet-iron. A slit was opened opposite the mantle, so that 

 the luminous rays which emanate from it might be directed 

 on to the aluminium sheet. Outside the lantern in front of 



he alummmm sheet was placed a biconvex lens of quartz, and 

 behind It an exciter giving little sparks. It was ascertained 

 that the spark is of greater or less clearness according to 

 the distance at which it is placed from the slit. M. Blondlot 

 proved the existence of four distinct kinds of radiations. 

 \V hen one directs a pencil of these rays either on to an 

 electric spark, or on to a little flame, or a phosphorescent 

 •substance previously exposed to light, one can see the li<'ht 

 emitted by these different sources increase in brilliancy 



The greater number of artificial sources of light and heat 

 emit X-rays. The sun emits them, as the following experi- 

 ment shows : A completely dark and closed room has a 

 window exposed to the sun, this window is shut by inside 

 oak shutters, 15 millimetres in thickness. Behind one of 

 these shutters, at a distance of i metre, is placed a tube of 

 fine glass, containing a phosphorescent substance of sulphu- 

 ret of calcium for example, previously slightly insulated. If 

 now in the trajectory of the sun's rays, which are supposed to 

 reach the tube through the wood, there is interposed a piece 

 of lead, or even simply the hand, even at a considerable 

 distance from the tube, the brightness of the phospho- 

 rescence diminishes. If one takes away the obstacle it re-ap- 

 pears. The interposition between the shutter and the tube 

 of several sheets of aluminium, of cardboard, of a piece of oak 

 three centimetres thick, does not prevent the phenomenon 

 from taking place. All possibility of heat radiation, properly 

 so called, is therefore excluded from hypothesis. 



Certain substances appear to have the power of storing up 

 X-rays, and afterwards emitting them ; but the rays appear to 

 penetrate a metallic mass, in this sense, very slowly. Thus, 

 if one side of a sheet of lead two millimetres thick has been 

 exposed to X-rays for some minutes, that side only has become 

 acti\e. An exposure of several hours is necessary for the 

 activity to reach the other side. .-Muminium wood, dry or 

 moist paper, paraffin have not the property of storing up 

 X-rays. Sulphuret of calcium has it. Having enclosed a 

 dozen grammes of this sulphuret in an envelope, and then 

 having exposed the envelope to X-rays, M. Blandlot proved 

 that its neighbourhood sufficed to reinforce the phospho- 

 rescence of a little lamp of sulphuret previously exposed to 

 light. This property explains why the increase of the phos- 

 phorescence of the action of X-rays takes an appreciable 

 time both to be produced and to disappear. Owing, in fact, 

 to the storing up of the X-rays, the different portions of a lump 

 of sulphuret mutually augment their phosphorescence, the 

 storing up is progressive, the store is not instantly exhausted, 

 so that when one directs the X-rays on to the phospho- 

 rescent sulphuret their effect slowly increases, and when they 

 are suppressed their effect is only gradually extinguished. 

 Following on the experiments made by M. Charpentier on 

 the emission of X-rays, experiments to which we shall return, 

 M. Blondlot conceived the idea that certain bodies might ac- 

 quire the property of emitting rays from compression. He 

 proved that pieces of wood, of glass, of indiarubber com- 

 pressed by means of a carpenter's vice, become, during the 

 compression sources of X-rays. 



Bodies which are themselves in a state of forced equilibrium, 

 or molecular strain, as tempered steel or hammered brass, are 

 spontaneous and permanent sources of X-rays. One can show 

 it by means of tlie phosphorescent screen, and by another in- 

 direct method — that of the increased action of a pencil of light 

 upon the eye when it is accompanied by X-rays. 



The shutters of the laboratorj- are almost closed, and the 

 face of the clock fixed to the wall sufficiently lighted for it to 

 appear faintly as an indeterminate grey stain upon the wall at 

 a distance of four yards. If the observer, without changing his 

 place, directs towards his eyes the N-rays emitted by a brick 

 or pebble, previously insulated, he sees the face whiten, distin- 

 guishes clearly its circular shape, and may e\en succeed in 

 seeing the hands. When the X-rays are suppressed the face 

 again darkens. Xeither the production nor the cessation of 

 the phenomenon are instantaneous. 



.\s in these experiments the luminous object is placed very 

 far from the .source of the X-rays, and as besides, in order that 

 the experiment should succeed, it is necessary that the rays 

 should be directed not towards this object, but towards the 

 e)-e, it follows that there is no question here of an increase of 

 the emission from a luminous body under the influence of X- 

 rays, but rather of the reinforcement of the action received by 

 the eye, which is due to the X-rays which are joined to the 

 rays of light. One can replace the brick by a sheet of 

 tempered steel. 



The energy that the emission of X-rays represents is 

 probably borrowed from the potential energy which corres- 

 ponds to the forced state of tempered steel. This expenditure 

 is doubtless extremely feeble, since the effects of the X-rays 

 themselves are so, and thus explains the apparently illimit- 

 able duration of the emission. A sheet of iron that is bent 

 so as to take a permanent deformation emits N-rays, but 



