168 Professor Forbes on the Polarization of Heat. 



polarized. When suitably modified, these rays are capable of in- 

 terfering like those of light. 



6. The characteristic law of depolarization in the case of light 

 holds in that of heat, viz. that the intensities in rectangular posi- 

 tions of the analyzing plate, are complementary to one another. 



7. As a necessary consequence of the above, confirmed by ex- 

 periment, heat is susceptible of circular and elliptic polarization. 



8. The undulations of obscure heat are probably longer than 

 those of light. A method is pointed out for deducing their 

 length numerically. 



78. Of the evidence for these conclusions I have enabled the 

 reader to judge, by specifying numerical results. But I must 

 farther add, that all the principal conclusions were arrived at by 

 the indications of the galvanometer, observed by the naked eye, 

 including the chief phenomena of depolarization. Since I thought 

 of the method of magnifying the divisions (described in (5),) I had 

 little else to perform than the agreeable task of verifying and de- 

 fining my first conclusions. 



Edinburgh, 

 19^ January 1835. 



