116 Notice of some Recent 



spect to thickness, conducting power, density, &c, and 

 referred to the experiments of Sir John Leslie, in which, 

 equal quantities of different radiating substances were dis- 

 solved, and spread upon a surface for comparison. Mr. 

 Bache answers, " that equal thicknesses of substances, 

 possessing different radiating powers, should be compared 

 together, seems to me, disproved by the law established 

 by Sir John Leslie's own experiments, viz., that radiation 

 takes place, not only from the surface, but in a thickness, 

 which is appreciated in good radiators. Thus, when dif- 

 ferent coatings of jelly were applied in succession upon one 

 of the sides of the cube, in Professor Leslie's experiments, 

 the radiation increased with the thickness up to a certain 

 point. The effect of the conducting power appears, by 

 the same experiment, to be so small, that an increase of the 

 thickness in the bad conductor was actually more than 

 eomjoensated for, by the increased radiating power. The 

 influence of density on conducting power is well known ; 

 but the effect of either, as controlling the radiating power 

 of a substance, or as modifying it, is, I apprehend, yet to 

 be appreciated." 



Mr. Bache employed, in his experiments, tin cylinders 

 2 inches high, and 1-J in diameter, closed at the bottom 

 with a slightly conical tube fitted to the top, to receive 

 a perforated cork, through which the stem of a thermo- 

 meter was admitted. The colouring matter, whose in- 

 fluence on the radiation was to be determined, was applied 

 to the cylinder, which was filled with hot water, and the 

 time of cooling noted. The results which he obtained are 

 decidedly unfavourable to the specific effect of colour in 

 determining the radiating powers of bodies. In one set 

 of experiments exhibited in a table, blue is above black 

 in the beginning of the table, and occurs again at the 18th 

 place. Although the first seven numbers were blue or 

 black, the 9th, 10th, 11th, and 12th were white, black, blue 

 and white respectively. White is in the greater number 

 of cases in the middle part of the table, ranging close to 

 black. Hence, it is concluded, that the alleged advan- 

 tages of dark clothing, during cold weather, has been too 

 hastily inferred ; and that, if a person is not exposed to the 

 sun, the particular colour of the clothing is not of real con- 



