230 Historical Review of Experiments 



with spirit of wine, there was nothing besides this 

 fluid, in the second there was a mixture of spirit of 

 wine and eider-down, and in the bulb of the third ther- 

 mometer there was a mixture of spirit of wine and flat- 

 tened silver threads. 



If, then, I exposed these thermometers in turn, now 

 to the influence of the rays of the sun, and again to the 

 influence of rays coming from bodies warmed by the 

 fire, I could, from the rapid or gradual heating of the 

 different thermometers, arrive at a sufficiently just con- 

 clusion with regard to the identity of the radiations or 

 to the difference between them. 



It would be too tedious if I were to describe these 

 experiments here in detail. From some of them I 

 obtained many, in certain respects, very remarkable 

 results,* which allowed me to draw such conclusions as 

 pointed out clearly enough the way in which I must 

 proceed towards the chief object of my researches. 



I afterwards procured other thermometers of very 

 large size. Their bulbs are round, and are made of 

 copper ; they are four inches in diameter. Their tubes, 

 which are glass, are thirty inches long, and are filled 

 with linseed oil. I use them in experiments designed 

 to determine the relative rapidity with which a warm 

 body (the thermometer itself) cools in different liquids 

 having the same temperature. This instrument is the 



* I noticed, among other things, that the thermometer whose bulb contained a 

 mixture of spirit of wine and flat silver threads was much more sensitive in general, 

 and especially to very slight changes of temperature, than another thermometer of the 

 same size, the bulb of which contained only spirit of wine. It would, perhaps, be of 

 advantage to procure similar thermometers to use, if not ordinarily, at least on certain 

 occasions. I am firmly convinced that a thermometer whose bulb is filled with 

 mercury and platina cut into threads will be much more sensitive, that is, will indicate 

 the temperature much more quickly, than a thermometer of the same size filled, as is 

 usual, with mercury alone. 



