May 15, 1896.] 



SCIENCE. 



729 



themselves. If, for example, we let the 

 cathode raj's fall on a plate, one-half con- 

 sisting of a 0.3 mm. sheet of platinum and 

 the other half of a 1 mm. sheet of aluminum, 

 a pin-hole photograph of this double plate 

 will show that the sheet of platinum emits 

 a far greater number of X-rays than does 

 the aluminum sheet, this remark applying 

 in either case to the side upon which the 

 cathode rays impinge. From the reverse 

 side of the platinum, however, practically 

 no X-rays are emitted, but from the reverse 

 side of the aluminum a relatively large 

 number are radiated. It is easy to con- 

 struct an explanation of this observation ; 

 still it is to be recommended that before so 

 doing we should learn a little more about 

 the characteristics of X-rays. 



It must be mentioned, however, that this 

 fact has a practical bearing. Judging by 

 my experience up to now, platinum is the 

 best for generating the most powerful X- 

 rays. I used a few weeks ago, with excel- 

 lent results, a discharge apparatus in which 

 a concave mirror of aluminum acted as 

 cathode and a sheet of platinum as anode, 

 the platinum being at an angle of 45 deg. 

 to the axis of the mirror and at the center 

 of curvature. 



§ 21. The X-rays in this apparatus start 

 from the anode. I conclude from experi- 

 ments with variously-shaped apparatus that 

 as regards the intensity of the X-rays it is 

 a matter of indifference whether or not the 

 spot at which these rays are generated be 

 the anode. With a special view to re- 

 searches with alternate curi'ents from a 

 Tesla transformer, a discharge apparatus is 

 being made in which both electrodes are 

 concave aluminum mirrors, their axes be- 

 ing at right angles; at the common center 

 of curvature there is a ' cathode-ray catch- 

 ing ' sheet of platinum. As to the utility 

 of this apparatus I will report further at a 

 later date. 



W. K. EONTGEN. 



BEEAVIOB OF SUGAR TOWARDS RONTGEN 

 RAYS. 



The fact that sugar is transparent to 

 X-rays was ascertained at an early date 

 after Eontgen's announcement of his mo- 

 mentous discovery. It seemed, however, 

 of interest to learn whether the structure 

 of the sugar traversed by the rays might 

 exercise any influence on the rays or modify 

 their action on photographic plates. 



Through the courtesy of Prof M. I. 

 Pupin, of Columbia University, who kindly 

 extended the privileges of his laboratory to 

 the writer, the following tests were made : 



Two plates of sugar were selected. The 

 one was a disk 16 mm. thick, sawed from a 

 titlar; a titlar is made by pouring a magma 

 of best white refined sugar into a cone- 

 shaped mould, washing well with pure 

 white sugar liquor, and then baking the 

 mass perfectly dry and hard. This disk 

 was, therefore, practically a solid agglom- 

 eration of pure sucrose crystals. The other 

 disk was made by dissolving perfectly pure 

 white sugar in water, evaporating to a cer- 

 tain consistency, and then casting the mass 

 in a copper ring. This disk also measured 

 16 mm. in thickness; it was a perfectly 

 clear and transparent solid of a yellow 

 color, and consisted of amorphous sugar- 

 candy— so-called barley sugar. 



A few preliminary trials were made by 

 photographing with X-i-ays through these 

 plates of sugar — with and without fluores- 

 cent screens — varying the time of exposure, 

 etc. Finally, the following experiment was 

 carried out. 



A photographic plate was placed in a 

 box, on the outside of which six metal disks 

 were arranged in two groups of three each. 

 Each group consisted of a medal of alumin- 

 ium, provided with figures and inscrip- 

 tions in bas-relief, a plain disk of aluminium 

 and a silver quarter dollar. 



One of these groups was covered with the 

 crystalline, the other with the amorphous 



