OF ARTS AND SCIENCES. 125 



Investigations on Light and Heat, made and pcmLisnED wholly oe in paet with 

 Appbopriation prom the Rumford Fond. 



XII. 



AN ACCOUNT OF A NEW THERMOGRAPH, AND OF 

 SOME MEASURES IN LUNAR RADIATION. 



By C. C. Hutchins, assisted by Daniel Edward Owen. 



Presented by Professor Trowbridge, March 13, 1889. 



During the winter of 1886-87 the writer carried out at Cambridge 

 a series of experiments with the bolometer and other sensitive heat- 

 measuring devices, the intention being, if the apparatus could be made 

 to perform satisfactorily, to attempt the solution of some problem in 

 radiation. One in particular in mind was that of the radiation from 

 rocks, as important from a geological standpoint. It was also thought 

 possible that the work might be made a valuable supplement to Lang- 

 ley's investigations in lunar radiation. 



After two or three months of preliminary experimentation the 

 matter was abandoned, and the further pursuit of the subject was not 

 undertaken until October, 1887. In designing a working apparatus 

 for use in the research thus resumed, some modification of the thermo- 

 pile suggested itself, and a contrivance was finally adopted constructed 

 upon the principle embodied in that familiar instrument. This new 

 device possesses the sensitiveness necessary for accurate and delicate 

 work, and at the same time is very simple in operation. This last is 

 an important feature, for in all instruments intended for measuring 

 small quantities of heat the matter of simplicity is a very grave one. 

 It hardly needs saying, that the number of the parts in the instrument 

 should be limited to as few as possible, and that the whole should be 

 as simple as it can be made. Multiplication of parts leads to inaccu- 

 racy in performance with almost absolute certainty. It is the element 

 of simplicity that has, until recently, rendered the ordinary thermopile 

 the most successful instrument possible to be employed in dealing with 

 small quantities of heat. The failings of the thermopile, however, 

 are so numerous and so fatal that it becomes an instrument of precis- 

 ion in the hands of a very few, who must serve a long apprenticeship 

 in its use. 



