ART OF WRITING IN THE DARR, " 53 



A, there pafTes a Iblid cylinder, of which the lower part B fpace for water 

 (diminiftied in diameter) pafles out through another collar of j" reduced to^ 

 leathers D ; the internal fpace or pump barrel lituate between that of a much 

 thofe two collars being clofed on all fides, except where two *"^*'^'^* :^ 

 pipes communicate, one of which, E, has a valve opening in- 

 wards, and the other D, has a valve opening outwards. Now 

 when the folid cylinder or plunger is drawn up, the larger 

 portion pafles for the raoft part out of the cavity of the barrel; 

 but in (lead of being replaced by an equal mafs of water enter- 

 ing through the pipe E as ufual in the jack head pump, it is 

 inoftly replaced by the introduAion of the folid part B, and the 

 water which enters will be equal in its folid contents to the 

 difference only between the folidities of the two cylindrical 

 parts of the fame length. Or the q^q^ will be the fame as if 

 the barrel were of much fmaller dimenfions. In this way with 

 the ftrength of conftrudion and ample fittings of a large engine 

 the power of a fmall one may be obtained, which in fome vor 

 ilances of forcing may be defirable. 



It fcarcely need be mentioned that the fame efFe6l may be 

 produced by two folid piftons working in diftinft barrels of 

 diflerent bore or ftroke, and communicating with each other. 



X. 



Scoteography, or the Art of Writing in the Dark, In a Letter 

 /rom ikfr. John GouGH , 



Tp Mr. NICHOLSON. 

 SIR, 



JTERHAPS you have remarked that my communications to Hlftory of th^ 

 your Journal are not all in the fame hand : the truth is, I am ^^vefttion. 

 unable to write; and my ignorance of the art arifes from the 

 lofs of fight in early infancy. The knowledge of the preced- 

 ing circumftance cannot prove of the leaft moment to you ; 

 It is only mentioned by way of introduflion to the prefent let- 

 ter, which may afford an ufeful hint to perfons labouring un- 

 der the fame difadvantage. 



The perufal of Mr. Berard's method* of teaching the blind 



* Phil. Jour, Nov. 1802, Vol. IIL page 190* 



to 



