252 Mr. G. Dakin's proposed Improvements in the Construction 



and immediately lined and covered with shell-lac, as this sub- 

 stance stands the very first on the list of electrics and insula- 

 tors*. This practice, it appears to me, would be much better 

 than that of insulating the cylinder, as the glass rods are so apt 

 to get loose or broken. The cylinder represented in the figure is 

 mounted in the usual way ; but instead of terminating with the 

 small wheel, there is a round projecting part with a bayonet catch 

 on it, and the same on the multiplying-wheel. The crank is 

 formed hollow like the handle of a bayonet, and fits both these; 

 so that incase of the catgut breaking, it can be immediately fixed 

 to the cylinder. Thus the advantages of the crank- and mul- 

 tiplying-wheel machine are combined ; for when the amalgam 

 is first applied, the friction is much too great for the catgut to 

 overcome without stretching or breaking ; and then it must be 

 tightened, or the second string must be applied ; and in cases 

 of suspended animation it causes a serious interruption, even 

 if this is at hand. The rubber is made in the usual way ; but 

 instead of a chain the communication with the earth is made 

 with wire, and two balls, which are in contact when the 

 prime conductor is positive, and separate or entirely removed 

 when the negative conductor is used. With respect to the 

 silk flap, my observation goes no further than this; — that I be- 

 lieve the varnished silk will keep a machine longer in mo- 

 derate action in a damp room, but that unvarnished silk will 

 adhere closer, and produces a greater effect in a dry room. 

 The bottom of the machine should be continued the whole 

 length of the conductor, as it contributes so much to the 

 steadiness of the whole of the apparatus, that a person who 

 has once been used to it would never tolerate any other. Be- 

 sides, it does not take so much material to make it; for there 

 is no necessity for a stand for the conductor, a bottom for 



* In the Phil. Mag. and Annals, vol. v. p. 171, will be found an account 

 of a globe electrical machine of uncommon power, constructed of black 

 or green bottle-glass by the Rev. J. B. Emmett. In chemical operations, 

 instruments and vessels of this kind of glass would be more useful even 

 than in electricity, but the existing provisions of the Excise Laws do not 

 permit their use : we add a paragraph on this subject from Mr. Faraday's 

 " Chemical Manipulation," in the hope of assisting to draw attention to it, 

 and of promoting by that means such alterations in the laws as may en- 

 able the cultivator of science to obtain apparatus formed of this useful 

 material. Mr. Faraday observes, p. 226, " It is much to be regretted that 

 the chemist cannot obtain glass retorts and other vessels which have 

 to resist high temperatures, of green bottle-glass, and of all the forms and 

 sizes he requires. Large glass retorts, for the purpose of concentrating 

 sulphuric acid, are made of it ; but much smaller ones, from two pints to 

 an ounce in capacity, are required in the laboratory of research. Even 

 green glass tubes are rarely to be procured, and are not permitted to be 

 made without the special leave of the Board of Excise." — Edit. 



the 



