Mr. G. Dakin on the Cylinder Electrical Machine. 251 



therefore probable that this partial pressure, which only exists 

 in the lower regions, may be the cause of the difference of the 

 following admeasurements of the Peak. 



Barometrical admeasurements of the Peak, after the formula of Laplace. 



Father Feuille in 1724 12,957 feet 



M. Borda in 1776 12,646 



MM. Lamanon and Monges in 1 785 1 2, 1 79 



M. Cordierin 1803 12,284 



Professor Smith in 1815 12,188 



Baron Von Buch, calculated by Dr. Savinon . . 12,131 



Geometrical admeasurements. 



Father Feuille in 1724 (his base was too small) 14,159 



Dr. Heberden in 1752 (several operations) .. 13,192 



Hernandez in 1742 15,407 



Borda and Pingre in 1771 (an error in the cal- 

 culation) 1 1,337 



Borda in 1776 12,188 



Taken under sail. 



Mauneville in 1749 1 2,796 



Borda and Pingre in 1 77 1 10,883 



Chunucain 1788 14,031 



Johnston 12,943 



[To be continued.] 



XLI. Proposed Improvements in the Construction of the Cy- 

 linder Electrical Machine and accompanying Apparatus. By 

 Mr. G. Dakin. 



To the Editors of the Philosophical Magazine and Annals. 

 Gentlemen, 



f HAVE sent you a drawing of some improvements which 

 - I have lately made in the cylinder electrical machine for 

 medical purposes, and which would also be found well adapted 

 for the usual routine of electrical experiments. There is one 

 very great drawback in the study of electricity ; and that is, 

 that many persons who are possessed of large cylindrical ma- 

 chines are unable to produce the effects of others of perhaps 

 not half the size : the fact is, that all glass is not fit for this 

 purpose, most probably owing to a slight excess of alkali in its 

 composition. Some of the most refractory cylinders will re- 

 quire to be warmed, greased, and well excited with a large 

 piece of silk or a coarse towel. Now as the common black 

 glass, such as wine bottles are made of, appears to be well 

 adapted for this purpose, I would recommend that cylinders, 

 plates, jars, and rods, should be made of this sort of glass, 



2 K 2 and 



