C.omparifon between Cylinder and Plate Machines for Eleclricity. 83 



that the above fpirltuous flimuli have been found of fervice in countera£\ing it. The 

 ftiraulus of food, taken even againft the inclination, has alfo been frequently found to be 



beneficial. 



VII. 



A Comparifm betivten Ele^rical M.ichims iv'itha Cy'injer, and ihofe which produce their Effccl hy 

 means of a Circular Plate of Glafs. With a Dcfcription of a Ahchir.e of great Simplicity and 

 Poiver, invented hy Dr. MaRTINUS Van MaruM. 



J.T is a remarkable circumftance that the plate-machine for eletlricitj', firft invented and 

 publiflied in this country by Dr. Ingenhoufz, has never been much iifed here, though it has 

 been well received on the Continent, and aimoft univerfally preferred to the machine with 

 a cylinder. Tliis may in fome meafure be owing to the improvements in our manufaflure 

 of blown glafs, by which we have been fupplied with cylinders of confiderable dimenfions 

 at a moderate price, inftead of the globes which were originally ufed for this purpofe. Some 

 years ago (1787) I improved the cylinder-machine by a contrivance for changing the eleflri- 

 city of the conduftor from plus to minus almoft inflantly, which is defcribed in the Philofo- 

 phical Tranfaftions for 1789. From a comparifon of the quantities of eleftricily accumu-- 

 lated by the fritlion of a fquare foot of glafs, I was induced to adopt the opinion, that cylin- 

 ders were preferable to plates in every refpeft, excepting the great quantity of furfacc 

 afforded by the latter in machines conftrufted without Kgard to expence. The labours of 

 the celebrated Dr. Van Marum, together with fome obfervations of my own, have fince 

 that time tended to alter my opinion : for which reafon I (hall, in the firft place, enume- 

 rate a few general fa£l:s, and then proceed to defcribe his excellent improvement of my con- 

 trivance. 



I. Eleftvical«machines were formerly made to revolve with confiderable velocity by a mul- 

 tiplying wheel. 'J his has fince been rejefted in confequence of the ftrong excitation and 

 increafed friilion produced by a more advantageous application of the amalgam of zinc and 

 mercury. The machines with a finglc winch demand the fame labour as before to work them. 

 They exhibit much more fire in the form of flaflies and fparks. But, as far as my experience 

 fhews, the fpark from the old machine was denfer and more pungent, the excitation more 

 rteady, and the time employed in charging fomewhat fhorter. 



n. A cylinder with a fingle winch requires larger terminations of its metallic parts to 

 prevent the fire fi om (ladling out, than are required cither in the old machine, or one of thofe 

 conftrufted with a flat plate. 



III. It frequently happens that the fimplc machine will be in a flate to throw out ramifi- 

 cations ta the table, to the face of the operator, and into the air ; though the aclual fpark 

 is not very denfc, nor the power great, when examined by the time required to charge a bat- 

 tery or jar. 



IV. From thcfe circumdances it appeared prcbablc that the cleiflric matter in a charged 

 conductor may be tjirown into a ftate of undulation by an irregular fupply from the cylinder, 

 and that in this ftate it will fly off more readily tlian when fupplied hy a moro uniform ftream. 

 Thus, when the cylinder is of an irregular figure, the adion of the cufliion will be ftronger 



M 2 on 



