128 MEMOIR OF DR. DALTON, AND 



less ; nor is it more essentially a body, when solid, as ice, than 

 when fluid ; that is, the minims of it are equally disposed to 

 motion or rest in position to each other ; and therefore body, 

 as body, may as well be, or be supposed to be, indefinitely 

 fluid as definitely solid ; and, consequently, there is no 

 necessity to suppose atoms, or any determinate part of body 

 perfectly solid, or such whose parts are incapable of changing 

 position one to another ; since, as I conceive, the essence of 

 body is only determinate extension, or a power of being un- 

 alterable of such a quantity, and not a power of being and 

 continuing of a determinate quantity and a determinate figure, 

 which the anatomists (or atomists) suppose. These, I con- 

 ceive, the two powers or principles of the world, to wit, 

 body and motion^ uniformity of motion making a solid, and 

 diffbrmity of the motion of the parts making a fluid, as I 

 shall prove more at large by and by." 



* * * * " As for matter^ that I conceive in its essence 

 to be immutable, and its essence being expatiation deter- 

 minate, it cannot be altered in its quantity, either by con- 

 densation or rarefaction ; that is, there cannot be more or less 

 of that power or reality, whatever it be, within the same 

 expatiation or content ; but every equal expatiation contains, 

 is filled, or is an equal quantity of materia ; and the densest 

 or heaviest, or most powerful body in the world contains no 

 more materia than that which we conceive to be the rarest, 

 thinnest, lightest, or least powerful body of all ; as gold for 

 instance, and cether, or the substance that fills the cavity of 

 an exhausted vessel, or cavity of the glass of a barometer 

 above the quicksilver. Nay, as I shall afterwards prove, this 

 cavity is more full, or a more dense body of aether, in the com- 

 mon sense or acceptation of the word, than the gold is of gold, 

 bulk for bulk ; and that because the one, viz., the mass of 

 sether, is all aether ; but the mass of gold, which we conceive, 

 is not all gold, but there is an intermixture, and that vastly 

 more than is commonly supposed, of sether with it ; so that 



