XOVUM ORGANUM. 115 



36. The irritation of surrounding cold increases heat, as 

 may be seen in fires during a sharp frost. We think that this 

 is owing not merely to the confinement and compression of 

 the heat (which forms a sort of union) ; but also by the 

 exasperation of it, as when the air or a stick are violently 

 compressed or bent, they recoil, not only to the point they 

 first occupied, but still further back. Let an accurate ex 

 periment, therefore, be made with a stick, or something of 

 the kind, put into the flame, in order to see whether it be 

 not sooner burnt at the sides than in the middle of it.* 



37. There are many degrees in the susceptibility of heat. 

 And, first, it must be observed how much a low gentle heat 

 changes and partially warms even the bodies least suscep 

 tible of it. For even the heat of the hand imparts a little 

 warmth to a ball of lead or other metal held a short time in 

 it. So easily is heat transmitted and excited, without any 

 apparent change in the body. 



38. Of all bodies that we are acquainted with, air admits 

 and loses heat the most readily, which is admirably seen in 

 weather-glasses, whose construction is as follows. Take a 

 glass with a hollow belly, and a thin and long neck ; turn 

 it upside down, and place it with its mouth downwards into 

 another glass vessel containing water; the end of the tube 

 touching the bottom of the vessel, and the tube itself lean 

 ing a little on the edge, so as to be fixed upright. In order 

 to do this more readily, let a little wax be applied to the 

 edge, not however so as to block up the orifice, lest by 

 preventing the air from escaping, the motion, which we shall 

 presently speak of, and which is very gentle and delicate, 

 should be impeded. 



Before the first glass be inserted in the other, its upper 

 part (the belly) should be warmed at the fire. Then upon 

 placing it as we have described, the air (which was dilated 

 by the heat), after a sufficient time has been allowed for it 

 to lose the additional temperature, will restore and contract 

 itself to the same dimensions as that of the external or 

 common atmosphere at the moment of immersion, and the 

 water will be attracted upwards in the tube to a propor 

 tionate extent. A long narrow slip of paper should be at 

 tached to the tube, divided into as many degrees as you 



* If condensation were the cause of the greater heat, Bacon concludes the 

 centre of the flame would be the hotter part, and vice versa. The fact is, neither 

 of the causes assigned by Bacon is the true one ; for the fire burns more quickly 

 only because the draught of air is more rapid, the cold dense air pressing rapidly 

 into the heated room and towards the chimney. 



