Improvements in Science. llo 



necessary, that every part of the figures which is not bow- 

 ing shall be at an absolutely equal distance from the centre 

 of the plate, and from the opening in the periphery, and 

 also, that the figures possess equal thickness and colour. 



2. Photometer of Maistre,* — This instrument consists of 

 two equal prisms laid upon each other, so as to form an 

 even plate. One prism is formed of dark blue glass, and 

 where the acute angle lies upon the base of the white 

 prism, the diameter of the blue glass is small, and then 

 constantly increases to the point where the edge of the 

 white prism lies upon the base of the blue. By a compari- 

 son of unequal parts of the prism, where the light ter- 

 minates, a comparison is obtained between the different 

 intensities of light. Quetelet has formed a photometer 

 upon a similar principle. 



3. Influence of Colour on the radiation of non-luminous heat. 

 — In 1833, Dr. Stark published an experimental inquiry on 

 the alleged influence of colour on the radiation of non- 

 luminous heat.f Mr. Powell, of Oxford, soon after objected 

 to these experiments,} considering them inapplicable. 

 Professors Bache and Courtenay, of the University of 

 Pennsylvania,^ have, since the publication of Dr. Stark's 

 paper, taken up the investigation, and confirm the objec- 

 tions, in some measure, of Mr. Powell, especially, in re- 

 ference to the experiments upon the absorption of radiant 

 heat, as tested by the inverse of Count Rumford's method 

 for comparing the conducting powers of substances used 

 for clothing ; also, as tested by the effect of the heat from 

 the flame of an argand gas burner, thrown by a mirror 

 upon the bulb of an air thermometer which was variously 

 coated. Of the same class, also, were the experiments on 

 radiation as tested by the method used by Count Rumford 

 already mentioned ; the enveloping materials of the inner 

 thermometer being wools of different colours, and coloured 

 wheat paste. An unexceptionable mode in the view of Mr. 

 Bache, which was adopted by Dr. Stark, was that of filling 

 a glass globe with hot water; and covering it with different 

 pigments. Mr. Powell disapproved of this method, unless 

 the radiating covering of the globe were equalized in re- 



• Jahresbericht, vi. 34. t Pliilos. Transact., 1833. 



t Kdinburfjli Journal. <j Journal of the Franklin Institute, November, -1835, 



i 2 



