PHENOMENA OF THE UNIVERSE. J 49 



sion of the smoky thread which ascends, (in the lowest 

 part before it is dispersed), and place the candle near the 

 fire, and again look at that portion of the fire which first 

 reaches it, you will not imagine that it exceeds more than 

 double the magnitude of the smoke. If you mark with 

 accuracy the dimension of gunpowder, or for greater cer 

 tainty measure it in a little box, and again take the dimen 

 sion of its flame after it has been lit, you will readily grant 

 that the flame exceeds the body (as far as it can be told at 

 first sight) a thousand degrees. And from what has been 

 before laid down, there should be a considerable proportion 

 of fire according to the nitre. But this I will explain more 

 perfectly in my observations upon this history. We very 

 clearly see that air itself is expanded and contracted from 

 heat and cold in those bodies of wind which physicians 

 use for attraction. For these warmed over the fire, and 

 then applied immediately to the body, draw the skin, the 

 air contracting itself and gradually recovering itself. And 

 this it does of itself, although the hemp may not have been 

 put on and heated, which is used to produce a more power 

 ful attraction. Moreover, if a cold sponge be applied out 

 side over the blister the air contracts itself so much the 

 more by virtue of the cold, and the attraction becomes 

 more determined. 



I have put a silver saltcellar of the usual bell-tower 

 form, in a bath or goblet filled with water, bearing the air 

 deprest with itself to the bottom of the vessel. I then put 

 two or three live coals in the little hollow space in which 

 the salt is placed when applied to its ordinary use, and 

 raised a flame by blowing. Very soon after, the air, rari- 

 fied by the heat, and impatient of its former orbit, lifted up 

 the bottom of the saltcellar on one side, and ascended in 

 bubbles. Hero describes an altar so constructed as that if 

 you laid a holocaust upon it and set it on fire, suddenly 

 water would fall to extinguish the fire. This might be 

 accomplished by air being received under the altar in a 

 hollow space closed up, and with no other way of exit 

 (when the air was extended by the fire) but where it might 

 force out the water prepared for this purpose, in the chan 

 nel. There were lately in this country some Hollanders 

 who had invented a musical instrument, which on being 

 struck by the rays of the sun gave out a certain harmony. 

 This was very probably owing to the extension of the 

 heated air which could produce the motion of the in 

 strument, since it is certain that air acted upon by the 



