IRANSACXIONS OF SECTION A. 465 



not convenient for practical purposes, it gave rise to the disc-cylinder integrator, 

 which is all that can be desired. This consists of a cylinder which is moved longi- 

 tudinally along its axis, while its surface is in contact with a disc. If the plane of 

 the disc is parallel to the axis of the cylinder, the latter will not rotate when moved 

 longitudinally ; if inclined, the revolution of the cylinder will be proportional to the 

 tangent of such inclination x the longitudinal movement. During the return stroke 

 of the cylinder, its surface must rest against a disc on the opposite side, that the 

 revolution may continue in the same direction. The double change of movement 

 is effected by a * mangle-motion,' driven by clockwork, and the inclination of the 

 discs by the beam of the indicator. The number of revolutions of the cylinder will 

 then be a measure of the total energy expended. The author felt hound to 

 mention that Professor Abdank Abakanowicz had previously invented an inte- 

 grator depending on the same mathematical principles, but, so far as he could learn, 

 had not applied them to practical purposes. The author had been accused, not by 

 Professor Abakanowicz, but by others, of pirating his invention ; but, as he had 

 never heard of it till he had completed his own, he was innocent of such a charge. 



Besides the simple integrator already explained, he described a series of machines 

 by which squares, products, quotients, and reciprocals may be directly integrated ; 

 among them is a polar planimeter, which is an exact mechanical translation of the 

 polar expression, \fr^-d6 ; but, as he had not yet applied them to practical purposes, 

 he did no more than allude to them. For the same reason he referred only to the 

 apparatus for calculating efficiency ; i.e. apparatus that will automatically divide the 

 speeds with which two integrals are growing one into the other and continuously 

 I'ecord the quotient. 



Of the vibrating electric meter it is not possible to give an account in the space 

 of this abstract. 



5. On a new Electrical Contact Maker. By Professor H. S. Hele Shaw. 



The author first called attention to the want of an absolutely reliable, and at the 

 same time sufficiently sensitive, electrical contact-maker. Such an instrument is 

 often required to measure or control the relative motion of bodies in conjunction 

 with delicate clockwork. He then proceeded to discuss the ways in which such 

 contact may be made. In theory, there really is no distinction in the modes of 

 doing til is, but practically they may be separated into — 



(1) Relative motion of the two terminal surfaces, normal to both. 



(2) Motion tangential to both. 



(3) Motion compounded of these two. 



These modes were separately discussed, and also the various objections with all 

 when solid terminals are used. The use of a liquid terminal, with which the other 

 terminal, being solid, is brought into contact, obviates most of these objections. 

 Of all liquids, mercury is the only one which can practically be employed. There 

 are, however, two objections to its use which have prevented its being hitherto 

 adopted for more than temporary and experimental purposes. These are : — 



(1) The fact that it readily combines with oxygen on the passage of the 

 electric spark. 



(2) The difficulty of making a contact-maker of this kind portable. 



The earliest form of instrument in which the author had endeavoured to over- 

 come these difficidties, was then shown on a diagi-am and described. Its principle 

 of action is briefly this. A short glass tube, closed at the upper end (such as an 

 inverted test-tube), is filled with mercury, and inverted in a vessel of mercurv. 

 The mercury in the tube is then partially displaced by hydrogen gas. A very light 

 bent lever, consisting of a platinum wire, passes through the mercury into the 

 gaseous space, and there makes contact between the mercury below, and a smaller 

 quantity of mercury in an insulated capside above the other portion, but within the 

 tube. This lever works on a pivot, being actuated from the outside by the escape- 

 ment of an ordinary clock, and is extremely sensitive in its action. The positive 

 and negative poles of the terminals are respectively connected with the mercury in 

 the capsule and that in the vessel below. It is evident that, although the lever is 

 1882. H H 



