744 PHILOSOPHICAL TRANSACTIONS. [aNNO 1780. 



some weeks observation, it could be only deduced, that if the colours, with 

 which the balls of the thermometer were painted, were pretty like the prismatic 

 colours, those thermometers showed a greater degree of heat, whose colours 

 were nearer to the violet in the order of the prismatic colours, and contrary wise ; 

 but they were all, even that painted with white load, in some intermediate degree 

 between the blackened thermometer and the naked or unpainted one. If the 

 colours had not the proper degree of density, the effects were very different: 

 thus, a thermometer painted with a light blue, was lower than another thermo- 

 meter painted red with good carmine. 



Mr. C. here describes the method in which he made and adapted the scales to 

 his thermometers ; and concludes this paper with mentioning an experiment, 

 which, though not thermometrical, is yet useful in removing a wrong notion 

 some persons have concerning the effect of light. Having seen in some book 

 that the common black phosphorus, or Homberg's pyrophorus, was impaired by 

 light, he was desirous to try the truth of this assertion. Accordingly towards 

 the beginning of the last year he prepared some pyrophorus, and inclosed por- 

 tions of it in 3 glass tubes, which were immediately sealed hermetically, and on 

 the 20th of May, 1779, •^wo of them were suspended to a nail out of a window, 

 and the 3d was wrapped up in paper, and was inclosed in a box, where not the 

 least glimmering of light could enter. In this situation they were left for above 

 a year, after which he broke one of those that had been kept out of the window, 

 and that which had been in the dark; but the pyrophorus of each tube seemed 

 to be equally good, taking fire within about half a minute after being taken out 

 of the tubes, and exposed to the air on pieces of paper; which shows that nei- 

 ther the presence nor absence of light had injured it. 



END OF THE SEVENTIETH VOLUME OF THE ORIGINAL. 



END OF VOLUME FOURTEENTH. 



Erratum. — p. IQi, 1. 56, for unhappy read happy. 



C. anJ R. Baldwin, Printers, 

 New Bridge-Street, London 



