THE RONTGEN RAY AND ITS RELATION TO PHYSICS 577 



the anode. I had only the ordinary assortment of Crookes' tubes, and 

 one of the tubes had aluminum wires which were a millimeter apart. 

 In one of these the source of the rays was a point upon the anode 

 not upon the cathode at all. It was a very small point. The photo- 

 graphs which I obtained by that tube were sharper than any I had seen 

 before. They are so very sharp that in estimating the shadow of an 

 object I determined that the point could not have been a thousandth 

 of an inch in diameter. Therefore the source in this case was a very 

 minute point upon the anode, and that point was nearer the cathode, 

 and I suppose some of the cathode rays might have struck upon it, and 

 it might have obeyed the law that the point where these X-rays are 

 formed is the point on the anode where the cathode rays strike. 



I had another very interesting tube, and I was going to bring some 

 of the photographs here to-night; but I thought they were so small that 

 it would be almost impossible to see them. I tried the three cases in 

 this tube: First, the case where the cathode rays strike upon the anode. 

 In that case I got very many Rontgen rays. Then I tried the case 

 where the cathode rays strike upon an object a piece of platinum. I 

 did not get any rays whatever then. Now, some people say that they 

 come from the point where the cathode ray strikes. I did not get any 

 whatever in that case. In this case the cathode ray struck upon a piece 

 of platinum in the centre of a bulb, and no rays were given out by the 

 anode either. Therefore I seemed to have a crucial experiment in each; 

 I seemed to have the case where the cathode ray strikes upon the anode, 

 and I got lots of rays. Then I had the case where the cathode rays 

 strike on a piece of platinum, and I did not get anything at all. Then 

 where the anode itself was free and no cathode rays struck it, I did not 

 get anything from it. It seemed to me as if the source was most abun- 

 dant when the cathode ray struck upon the anode; and that is the 

 theory, we know, upon which nearly all tubes are formed at the present 

 time. You have the focus tubes in which you focus the cathode rays 

 upon the anode, and in that case you have a very abundant source of 

 rays; but I do not believe you ever could get as small a source of rays 

 as I got with that first tube, where I had a source of a thousandth of an 

 inch diameter. Having such a small source of rays, it gave me a limit 

 to the wave-length, if there were waves at all; it would give me a limit 

 to the wave-length of which I will speak in a moment. As to whether 

 there are any rays where the cathode rays strike on any other objects, 

 we know that there are very feeble ones. It seems to be almost neces- 

 sary in order to get an abundant source that you should have cathode 

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