290 On a Substance produced during, &c. 



oxygen ; and which, in conjunction with the effects produced 

 upon it by chlorine, lead me, for the present, to regard it as 

 a binary compound of carbon and hydrogen : in respect to the 

 proportions, however, in which these elements are combined, I 

 have not yet as been able to satisfy myself. 



Upon another occasion I hope to give some further details 

 respecting the above product ; and to examine another sub- 

 stance, which Mr, Jennings informs me he has obtained during 

 the rectification of coal tar. 



Royal Institution, 

 Dec. 20, 1819. 



Art. XII. On M. Carnot's Theory of Defence by 

 Vertical Fire. 



M. Carnot, influenced probably by motives which it is not 

 our business to expound or inquire into, has promulgated some 

 singular doctrines respecting the defence of fortified places by 

 vertical fire, a system which has long been acknowledged as 

 furnishino- an important accessory mean ; but not, we believe, 

 till M. Carnot's proposal, ever thought of as the basis of defence. 



Sir Howard Douglas has published a small tract, entitled, 

 " Observations on the Motives, Errors, and Tendency, of 

 M. Carnot's Principles of Defence," which has furnished us 

 with the following paragraphs ; and which may serve to remove 

 the erroneous impressions, which authority so high as that of 

 M. Carnot might otherwise produce. 



M. Carnot recommends, that the besieged should begin to 

 make use of vertical fire upon the commencement of the con- 

 struction of the third parallel ; and from that stage of the siege, 

 keep up an incessant discharge of musketry and four-ounce iron 

 balls, at great elevation, upon the enemy's works, so as to form 

 a rain (pluie) of shot upon the trenches. The iron balls to be 

 discharged from a number of 12-inch mortars, two of which are 

 placed in the salients of each bastion and ravelin, in the front, 



