Professor Forbes's Researches on Heat. 447 



2. The mode of publication which circumstances have led 

 me to adopt, requires that the author should from time to time 

 state how far fresh experiments, have justified his first conclusions, 

 and which, if any, he is prepared to sacrifice. A want of perspi- 

 cuity in this respect has led to considerable ambiguity in several 

 cases of progressive publication. 



3. It affords me, then, no small satisfaction to be able to state 

 that a persevering examination of the laws of polarized heat, un- 

 der the improved circumstances which experience put at my dis- 

 posal, has confirmed every general statement which my first paper 

 contained ; the numerical results there given, never professed to 

 be exact, nor will the more accurate ones now to be substituted, 

 disprove any general conclusions derived from these preliminary 

 investigations. 



4. I proceed, then, to detail the results which have been ob- 

 tained, defining more clearly the experimental laws already de- 

 veloped, and the new discoveries to which I have this winter been 

 led, reserving for another communication the detail of some far- 

 ther investigations not yet completed. 



§ I. On the Use of the Thermo- Multiplier. 



5. I have succeeded in rendering the application of the 

 thermo-multiplier considerably easier, and more delicate than 

 formerly. In my last paper, art. 5, I described the application 

 of the telescope to determine accurately the amount of the de- 

 viation of the needle of the instrument indicating degrees of tem- 

 perature. I have made the arrangement more permanent, placing 

 the instrument on one shelf of a solid press, and clamping a little 

 arm A, Plate, Fig. 1, carrying the telescope, and centered at 

 a point in the prolongation of a vertical line, passing through 

 the centre of the card of the galvanometer, to a shelf above, as 

 seen in the figure. The little arm bearing the telescope, there- 

 fore, traverses the divided part of the galvanometer carcL, just as 



