Ag6 On a Mlftale in Dr. Smyth's Treatife 



Thofe who wifh to cxercife themfelves in thefe experiments 

 may try to produce the figures fpoken of by Dr. Chladni, ii% 

 bis before-mentioned work, following his directions, and the 

 rules here given : but they muft not be difcouraged if the 

 figures are not produced on the firft trials; for, in general, to 

 learn the method of making the experiments requires fome 

 time. 



The above rules contain fome general laws which vibrating 

 furfaces follow j but as my object here was to give only a 

 (hort view of the manner in which experiments muft be made, 

 1 (hall not enter into a further explanation of thefe laws, as I 

 mean to treat the fubjeft more fully on fome other occafion. 



X. Communication from Mr. Ckuickshank, Chcmijl 

 to. the Ordnance, relative to a Mi/lake in the lajl Edition of 

 Dr. Smyth's Treatife on the Effects of Nitrous Vapour 

 in preventing and deftroying Contagion. With an Account 

 of the Methods now employed at Woolwich for fumigating 

 •with the Sulphurous Acid, and with Oxygenated Muriatic 

 Acid Gas. 



JO THE EDITOR OF THE PHILOSOPHICAL MAGAZINE, 



SIB, 



i N the laft edition of Dr. Smyth's Treatife on the effects of 

 nitrous vapour in preventing and deftroying contagion, I was 

 not a little furprifed to find, at page %i\, the following paffage, 

 in a letter to Dr. Percival, dated Auguft i, 1796 ; 



«< Whether this will apply to the fmall-pox, I cannot fay 

 ft from my own experience ; but I have been told by Dr. Rollo 

 i( furgeon to the artillery, and Mr. Cmickfliankprofeffor- royal 

 " of chemiftry to the academy, that it deftroys the miafma of 

 f* fmall-pox; and that, of two quantities of matter taken for 

 1* the purpofe of inoculation, one was expofed to the nitrous 

 f* vapour, the other not : the perfons inoculated with the 

 7 « firft 



