ANNUAL OF SCIENTIFIC DISCOVERY. 



It is evident that the only limit to the completeness of the vacuum 

 obtained by this process, arises from the difficulty of preparing car- 

 bonic acid gas perfectly free from air. This may be very nearly over- 

 come by adopting precautions which are well known to practical 

 chemists. When an extreme exhaustion is required, the gas-holder 

 should be filled with recently boiled water, and the first portions of 

 carbonic acid that are collected in it should be allowed to escape. 



The substitution of phosphoric for sulphuric acid would remove 

 the possibility of either aqueous or acid vapors being present even in 

 the smallest amount, but such a refinement will rarely be found 

 necessary. 



In the experiment just described, the theoretical residue of air 

 would be y-g-joinj" P ar t of the entire quantity in the receiver, 

 which would cause a depression of - 4 ^ of an inch. This result 

 must have been nearly realized. If the exhaustion had been carried 

 at each time to 0-2 inch, the residue by theory would have been only 

 "FirrioTo P ai *k But the experimental results will not continue to 

 keep pace with such small magnitudes. London, Edinburgh^ and Dub- 

 lin Philosophical J\Iayazine, Feb., 1852. 



ON THE INFLUENCE OF MATERIAL AGGREGATION UPON 

 THE MANIFESTATION OF FORCE. 



The following is an abstract of a paper read before the Royal Insti- 

 tution of Great Britain, Feb. 1853, by Dr. John Tvndall. There are 



* * 



no two words with which we are more familiar than matter and force. 

 The system of the universe embraces two things an object acted 

 upon, and an agent by which it is acted upon ; the object we call 

 matter, and the agent we call force. Matter, in certain aspects, may 

 be regarded as the vehicle of force ; thus the luminiferous ether is 







the vehicle or medium by which the pulsations of the sun are trans- 

 mitted to our organs of vision. Or to take a plainer case, if we set 

 a number of billiard balls in a row and impart a shock to one end of 

 the series, in the direction of its length, we know what takes place ; 

 the last ball will fly away, the intervening balls having served for the 

 transmission of the shock from one end of the series to the other. Or 

 we might refer to the conduction of heat. If, for example, it be re- 

 quired to transmit heat from the fire to a point at some distance from 

 the fire, this may be effected by means of a conducting body - - by 

 the poker for instance ; thrusting one end of the poker into the fire 

 it becomes heated, the heat makes its way through the mass, and final- 

 ly manifests itself at the other end. Let us endeavor to get a distinct 

 idea of what we here call heat; let us first picture it to ourselves as an 

 agent apart from the mass of the conductor, making its way among 

 the particles of the latter, jumping from atom to atom, and thus con- 

 verting them into a kind of stepping-stones to assist its progress. It 

 is a probable conclusion, even had we not a single experiment to sup- 

 port it, that the mode of transmission must, in some measure, depend 

 upon the manner in which those litttle molecular stepping-stones are 



