282 PHILOSOPHICAL TRANSACTIONS. [aNNO 17/8. 



I did not try to freeze the sap of the others. Now, since tlie sap of a tree, 

 when taken out, freezes at 32"; also, since the sap of a tree, when taken out 

 of its proper canals, freezes when the heat of the tree is at 31°; and since the 

 heat of the tree can be so low as 17" without freezing; by wliat power are the 

 juices of the tree, when in their proper canals, kept fluid in such a cold ? Is it 

 the principle of vegetation ? Or is the sap inclosed in such a way as that the 

 process of freezing cannot take place, which we find to be the case when water 

 is confined in globular vessels ? If so, its confinement must be very different from 

 the confinement of the moisture in dead vegetables; but the circumstance of 

 vegetables dying with the cold, and then freezing, appears to answer the last 

 question. These, however, are questions which at present I shall not endeavour 

 to solve. I have made several experiments on the seeds of vegetables similar 

 to those on the eggs of animals; but, as inserting them would draw out this 

 paper to too great a length, I will reserve them for another. 



III. *The Force of Fired Gunpowder, and the Initial Velocities of Cannon Balls, 

 determined by Experiments ; from which is also deduced the Relation of the 

 Initial Velocity to the IVeight of the Shot and the Quantity of Poivder. By 

 Mr. Charles Hutton, F. R. S., of the Military Academy at JVoolwich. p. 50. 



These experiments were made at Woolwich in the summer of the year 1775, 

 in conjunction with several able officers of the royal artillery at that place, and 

 other ingenious gentlemen. The object of them was the determination of the 

 actual velocities with which balls are impelled from given pieces of cannon, when 

 fired with given charges of powder. These experiments were made according to 

 the method invented by Mr. Robins, anrl described in his treatise, entitled. New 

 Principles of Gunnery, of which an account was printed in the Philos. Trans, 

 for the year 1743. Before the discoveries of that gentleman, very little progress 

 had been made in the true theory of military projectiles. His book, however, 

 contained such important discoveries, that it was soon translated into several of 

 the languages on the continent, and the celebrated Euler honoured it with a 

 very extensive commentary, in his translation of it into the German language. 

 That part of it has always been particularly admired which relates to the experi- 

 mental method of ascertaining the actual velocities of shot, and in imitation of 

 which were made the experiments related in this paper. Experiments in the 



* This paper was honoured witli die Royal Society's prize medal : the public delivery of which 

 to the author, and the pronouncing of an excellent appropriate oration on that occasion, on the 30th 

 of Nov., 1778, by Sir John Pringle, was the last act of this gentleman in his capacity of president 

 of the R. s. — He was immediately succeeded in tliat otfice by Sir Joseph Banks. 



The paper itself contains the first part of a series of artillery experiments, then projected. A 

 fiirther extension of them, as conducted in several years, vjas given in Dr. Hutton's Tracts, printed 

 in 1786; and a far more important part still remains unpublisiied in that autlior's possession. 



