86 MR. D. WINSTANLEY ON THE RADIOGRAPH. 



XII. The Radiograph. By D. Winstanley, F.E.A.S. 



Eead January 13th, 1880. 



I HAVE described already one of the several arrangements 

 whicli I have devised for the automatic registration of the 

 solar radiance*. The instrument in question places a lead 

 pencil on a sheet of paper and writes down therewith 

 when and for how long the sun may chance to shine^ but it 

 makes no record of the intensity of his rays. I will now 

 ask your attention to the description of another and much 

 more perfect apparatus, one which continuously records 

 the intensity of thermal radiation to which it is exposed. 

 This instrument I have called the '' radiograph.^-" It con- 

 sists essentially as follows : — A differential thermometer of 

 which the stem is circularly curved is mounted concentri- 

 cally upon a wheel of brass in a groove cut with that 

 object for its end. This wheel is supported with its plane 

 in a perpendicular position by a knife-edge of hardened 

 steel, which passes through its geometric centre and rests 

 on agate planes. The tube of the thermometer is partly 

 filled with mercmy (preferably through half its curve);, and, 

 for the reason given in my description of the simple sun- 

 shine-recorder, to which I have alluded, a little sulphuric 

 acid is introduced as well. If we now arrange it that the 

 centre of gravity of the solid portion of the system here 

 described shall be below the surface of the planes on which 

 it turns (and the apparatus is provided with adjustments 

 by means of which the point in question can be moved) it 

 is clear that the arrangement may be made to swing in 

 * Proceedings of Manchester Lit. and Phil. Soc, Not. 18th, 1879. 



