326 I'HILOSOPHICAL TKANSACriON-S. [aNNO 172g. 



in which it began to rise, as 850 to y45 nearly. But it appears by experiments, 

 that air rarefied by a heat which makes a retort red hot, is only increased in 

 bulk, or dilated, 3 times ; by the heat of boiling water only -|-^ or nearly two 

 thirds; and by the heat of the human body, such as will raise vapours plenti- 

 fully, only -ff or about -}-. The Dr. owns that his objection may be answered, 

 by supposing the spherule of water to be more increased in diameter, as 

 for example 20 times; because then if it be filled with air only i rarer than 

 common air, it will be specifically lighter, and capable of rising to a consider- 

 able height. 



To give this solution all its force, let us express it in numbers. Let a and 

 w, fig. 4, pi. 7, represent a particle of air, and one of water of equal bulk; 

 then will the weight of A be to the weight of w, as ] to 850, their bulks 

 being equal. If the particle of water be blown up into a bubble (w) of 20 

 times its diameter, then will its bulk be to its weight, as 8000 to 850, while a 

 sphere of air (a) of the same size, has its weight as well as bulk equal to 

 8000 : now if an air or aura, ^ rarer than common air, be supposed within the 

 watery bubble, to keep it blown, it will be the same as if -2- of the air of a was 

 carried into w, and then the weight of w would be increased by the number 

 6000 ; so that the shell of water being in bulk 8000, would be in weight 850 

 -j- 6000 = 6850, while an equal bulk of air weighed 8000, and consequently 

 the watery bubble would rise till it came to an air, whose density is to the 

 density of the air next to the surface of the exhaling water, as 6850 to 8000. 



This is the strongest way of stating the hypothesis. But to support it, the 

 following queries must be answered. 



Query 1. How comes the aura, or air in the bubbles, to be specifically 

 lighter than the air without them, since the sun's rays, which act on the water, 

 are equally dense all over its surface? 



Query 2. If it could be possible for a rarer air to be separated from the 

 denser ambient air, to blow up the bubbles, as bubbles of soaped water are 

 blown up by warm air from the lungs, while the ambient air is colder and 

 denser, what would hinder that cold air by its greater pressure, from reducing 

 the bubbles to a less bulk, and greater specific gravity than the air, especially 

 since cold can be communicated through such thin .shells, and the tenacity of 

 common water is very small when compared to that of soaped water, whose 

 bubbles, notwithstanding that tenacity, are soon destroyed by the pressure of 

 the outward air, as the air within them cools? 



Query 3. If we should grant all the rest of the supposition, yet this diffi- 

 culty will remain : if clouds are made up of hollow shells of water filled with 



