160 G. S. hham — Registering Solar 



Art. XEV. — A Registering Solar Radiometer and Sunshine 

 Recorder; by Geo. S. Isham, A.M., M.D. 



The object sought in making the machine about to be 

 described was to get some simple form of registering appara- 

 tus which would give values in different places that could be 

 compared, for that part of the total insolation of any place 

 which goes to make it a source of convection currents, or what 

 might be called the convectional potential of the place. To 

 get absolute values for this seems an almost impossible thing 

 to do, but if by any means reliable relative values can be ob- 

 tained they will for many purposes be quite as valuable in 

 studying the many problems of local winds, thunder storms, 

 etc. 



The black bulb is intended to represent any clod of earth or 

 average matter exposed to the direct rays of the sun, and to 

 all the winds that blow ; the ordinary vacuum case is left off, 

 as introducing far greater errors than it corrects. The shelter 

 fulfills the above conditions as nearly as I can make it; a typi- 

 cal exposure would be an entirely unprotected one close to the 

 ground. The position should be one that represents, as nearly 

 as possible, the average of the locality. 



The name solar radiometer is unsatisfactory, as it conveys 

 the idea of a good deal more, and also something less, than is 

 intended. Perhaps convectometer would, be better. Its uses 

 as a sunshine recorder, and as a means of measuring the heat 

 given to vegetation are self-evident. For the latter use it 

 would be better to color the tube green or treat it as De 

 Blanchis has done in his investigations. 



The machine has been given its present form as presenting 

 a curve which requires the simplest corrections, there being 

 no correction for pressure, specific gravity, or temperature. 

 It is also simple enough to be understood and successfully run 

 by persons not specially trained. 



The instrument, in part like the registering barograph of 

 Sprung, is made as follows : a long, straight scale beam C is 

 balanced in the middle on a knife edge, resting on the support 

 A. Each end of the beam supports on its upper side a per- 

 pendicular glass tube hung by a collar D fitted with knife- 

 edge bearings, the collar being fastened a little above the 

 middle point of the tube. These tubes dip into cups S, Si, 

 connected together by a tube and capable of being raised or 

 lowered by the screws T, Tl. One of these tubes is covered 

 with lamp-black above the collar. 



Suspended from the beam by a rigid rod, with a screw 

 thread on it, is the weight Q, by moving which balance may be 



