'17i PHILOSOPHICAL TRANSACTIONS. [aNNO 1 67 5-6. 



It may also be calculated, how many times this air has been compressed in 

 the powder; but this calculation is more uncertain than the former, because we 

 know not whether this air took up more or less than the fifth part of the space 

 which the powder possessed. But yet it is certain, that though it had even 

 taken up three-fourths of the whole room of the powder, and that the 14 

 grains of the other matter had taken up no more than the one remaining fourth 

 part, still this air would have been compressed about 300 times. To calculate 

 this, suppose that the space of a cubic foot can hold only 72 pounds of gun- 

 powder, which contain more than 14 pounds of air, by the foregoing calculus; 

 which quantity of air is therefore found inclosed in the three-fourths of a cubic 

 foot. Now this space usually contains but about six drachms of air ; wherefore 

 to make it hold 14 pounds of air, which is near 300 times six drachms, it must 

 needs be that the air be compressed near 300 times. 



There is reason to believe, that this compression is much greater, because a 

 cubic foot can hold much more than 72 pounds of powder, and because also 

 that the fifth part of the weight must not in appearance possess alone the three- 

 fourths, and all the rest take up no more than one-fourth of the space possessed 

 by all the powder. 



We should therefore make no difficulty to believe, that all the effect of gun- 

 powder comes from the air which is compressed therein, and especially in the 

 salt-petre ; for we have not observed that brimstone yields air. Possibly also 

 we may find in time, that all other fulminations, ebullitions, and fermentations, 

 that make such surprising motions, are nothing else but air compressed expand.,, 

 ing itself.* 



An Account of Tivo Books. N° 122, p. 549. 



I. Cours d'Architecture, enseigne dans 1' Academic Royale d' Architecture, 

 Premiere Partie; par M. Francois Blondel,-!- de 1' Academic Royale des Sciences, 

 &c. a Paris, 1675, in fol. 



* With these very curious experiments and deductions do nearly agree those of Mr. Robins, re- 

 corded in the Philosophical Transactions about 70 years afterward j and on which he founded his ce- 

 lebrated theory of the force of fired gunpowder; as we shall hereafter have occasion to notice in its 

 proper place. 



t Francis Blondel, a celebrated mathematician, architect, and military engineer, was born at 

 Ribemond, in Picai'dy, 1617. While yet but young, he was chosen regius professor of mathematics 

 and architecture at Paris. He enjoyed many honourable employments in the navy and army; and 

 was intrusted with the management of several negociations with foreign princes. He anived at tlie 

 dignity of marechal de camp, and counsellor of state, and had tlie honour to be appointed mathema- 

 tical preceptor to the Dauphin. Blondel was a member of the Royal Academy of Sciences, director 

 of the Academy of Architecture, and lecturer to the Royal College ; in all which situations he sup- 



