J 46 Scientific Intelligence. [August, 



clean. As a substitute for the tin, Mr. Millington proposes to 

 employ glazed white earthen ware ; it has a strong reflecting 

 surface ; is very easily kept clean, is not expensive, and might, 

 he conceives, be so fixed, as not to be liable to be broken. For 

 the purpose of disposing of the light in the most useful manner, 

 the lower surface of the reflector, which is placed over the lamp, 

 should either be flat or curved outwards, so as to disperse the 

 rays, unless the object be to concentrate the light in any parti- 

 cular spot, when a concave dish, forming a portion of a hollow 

 dish, may be used. 



VIII. On the Colour of Bodies. By M. Prevost. 



A new hypothesis respecting the cause of colour in bodies has- 

 been lately proposed by M. Ben. Prevost, according to which it 

 is supposed that the effect depends not upon reflection but upon 

 radiation. It was formerly supposed that the different rays 

 which compose white light, were all of them, except those which 

 produce the colour of the body, absorbed by it, whilst these were 

 reflected ; M. Prevost, however, conceives that coloured bodies 

 reflect a portion of the light in its white or compound state, and 

 that they decompose a part of that which penetrates their sub- 

 stance into two new parts, one of which remains in the body, and 

 the other radiates from all parts of their surface. The colour of 

 bodies, as we commonly see it, is rendered pale by the white 

 light which is mixed with it; but it may be deprived of this by a 

 series of mutual reflections and decompositions, so as consider- 

 ably to augment the intensity of the colour. If, for example, we 

 receive successively the image of a plate of gold which is. 

 polished and illuminated by a bright light, upon a second plate, 

 and this image upon a third, &c. we may, after 12 or 18 of these 

 successive reflections, procure a deep red orange, which is 

 probably the real colour of gold. By applying the same process 

 to copper, we procure a colour which approaches to that of scar- 

 let ; silver becomes of a beautiful yellow ; tinned iron exhibits a 

 yellow deeper than that which is generally ascribed to gold ; and 

 in short M. Prevost concludes from his experiments that there 

 is no metal which is properly white or grey ; but that they all of 

 them possess some decided brilliant colour. 



IX. M. Depretz' Experiments on the Cooling of Metals. 



A series of experiments have been performed by M. Depretz 

 on the cooling of metals, which appear to have been conducted 

 with considerable attention to accuracy. His object was to 

 examine their specific heat and their conducting power, which 

 points, although they had been made the subject of experiment, 

 he conceived had not been ascertained with correctness, because 

 the experimentalists had not been aware of the effects of radia- 

 tion from polished surfaces. He employed balls of metal, with 

 a cavity in the center adapted to a thermometer ; filings of the 

 metals were placed round the bulb so as to fill up the cavity, and 



