134: CORRELATION OF PHYSICAL FORCES. 



An objection to which the view I have been advocating ig 

 open, and a formidable one, is, the necessity involved in it of 

 an universal plenum ; for if light, heat, electricity, &c., be affec 

 tions of ordinary matter, then matter must be supposed to be 

 everywhere where these phenomena . are apparent, and con 

 sequently there can be no vacuum. 



These forces are transmitted through what are .called 

 vacua, or through the interplanetary spaces, where matter, if 

 it exist, must be in a highly attenuated state. 



It may be safely stated that hitherto all attempts at pro 

 curing a perfect vacuum have failed. The ordinary air- 

 pump gives us only highly rarefied air ; and, by the principle 

 of construction, even of the best, the operation depends upon 

 the indefinite expansion of the volume of air in the receiver ; 

 even in the vacuum which is formed in this, so great is the 

 tendency of matter to fill up space, that I have observed dis 

 tilled water contained in a vessel within the exhausted receiv 

 er of a good air-pump has a taste of tallow, derived from the 

 grease, or an essential oil contained in it, which is used to 

 form an air-tight junction between the edges of the receiver 

 and the pump-plate. 



The Torricellian vacuum, or that of the ordinary baro 

 meter, is filled with the vapour of mercury ; but it might be 

 worth the trouble to ascertain what would be the effect of a 

 good Torricellian vacuum, when the mercury in the tube is 

 frozen, which might, without much difficulty, be now effected 

 by the use of solid carbonic acid and ether ; the only proba 

 ble difficulty would be the different rates of contraction of 

 mercury and glass, at such a degree of cold, and more par 

 ticularly the contraction of mercury at the period of its 

 solidification. Davy, however, endeavoured to form a 

 vacuum, in a somewhat similar manner, over fused tin, with 

 but partial success ; he also made many other attempts to 

 obtain a perfect vacuum ; his main object being to ascertain 

 What would be the effect of electricity across empty space : 



