MEDICAL BATTEPvIES. 61 



" This general arrangement of tbe instrument greatly simplifies 

 its manipulation, and will promote the extended employment of 

 the continuous current. 



'• A pair of elements with chloride of silver, having eight square 

 centimeties of working zinc surface, will correspond, as regards 

 quantity, to a new and well charged pair of Kemak's. The electro- 

 motor force is a little less, about in the ratio of 5 to 6. In order 

 to obtain the equivalent of a cumbrous Eemak's battery of 24 

 pairs, it is sufficient to have 36 pairs of chloride of silver with 

 eight centimetres of surface. 



" Lastly, the cost of the battery does not exceed thirty centimes 

 the working hour, when the human body forms part of the circuit." 



I have now experimented with this battery for about a month, 

 and have been well satisfied with the results obtained. Its 

 transport is as easy as that of an induction instrument ; and its 

 application requires none of the manipulation inevitable in the 

 use of other batteries ; but I have not had it under observation 

 sufhciently long to be able to determine its actual value, or to say 

 how far it fulfils the promises of the inventor with regard to its 

 electro-motor force, and with regard to the constancy of its con- 

 tinuous current. 



(h). Small columnar j^ile of the Conservatoire des Ai'ts et Metiers.— 

 There has long been made in England a small columnar battery 

 (a diminutive of Volta's pile), of which each disk, formed of two 

 plates of copper and zinc soldered together, has a diameter of 

 about one centimetre and a half. This battery is formed of a 

 greater or less number of couples. The disks, and the circles of 

 cloth wliich separate the couples, all have a central perforation, by 

 which they are strung on to a cotton wick, so as to form a little 

 column. To excite tlie battery, the whole is dipped in vinegar. 

 The circles of cloth and the cotton wick remain impregnated with 

 the liquid for some time after they are withdrawn from it. The 

 current of this pile is sufficiently steady ; because the acid used 

 (vinegar) attacks the metal plates slightly. 



This little pile occupies only a small space, but it requires to be 

 cleaned after every time of using, and thus occasions much loss of 

 time. From the number and the small surfaces of its elements, it 

 increases the physiological power of the battery while diminishing 

 its bulk and calorific action. This was evidently an improvement, 

 the utility of which, unfortunately, was little understood, for the 

 apparatus has remained almost unknown; and the idea which 

 governs its construction has been too long neglected. 



[Hammond's columnar lattery.— Dv. William A. Hammond, of New York, 

 has devised a very ingenious columnar battery, of the effects of which he 



