26 R. a. WEST ON A NEW UNIVERSAL-MOTION 



movement involves a lateral and vertical displacement of the object, 

 which is thus continually thrown out of the field and out of focus. 



Now, it occurred to me that if I could place the object in the 

 centre of the movable sphere, all lateral displacement would be 

 abolished, and the small inevitable focal displacement of the margin 

 of the object would be reduced to a minimum, while its centre would 

 remain absolutely undisturbed. My first idea was to place the 

 object-carrying plate on a segment of a sphere of soft iron or 

 steel. This rested on a magnetic post let into the base-plate, and 

 with its U23per surface turned to a concavity to fit the spherical 

 segment. The magnet might be made of horse- shoe form, with 

 the spherical segment of iron or steel as a keeper. The segment 

 was so much less than a hemisphere, that the combined thick- 

 ness of the carrying plate, the slide and an object of moderate 

 size would place the upper surface of this last approximately in the 

 centre of the sphere. It is obvious that, with the low powers for 

 which all these appliances are chiefly useful, this would meet the 

 requirements of the case in respect of the immobility of the object. 

 It was not put to the test of construction ; but my only fear re- 

 specting it is lest the magnetism should prove not thoroughly equal 

 to its work, and so make occasional shipwreck of a slide. 



For carrying out my idea in another form I am indebted to the 

 ingenuity of my friend, Mr. Henry W. Wimshurst, as I am to his 

 mechanical skill for the construction of the specimens now sub- 

 mitted to you. One of these is represented in vertical section in the 

 diagram, fig. 1, plate II. In this figure A A is a base-plate formed 

 with a small boss B in its centre. To this plate is soldered a short 

 brass tube C C. In the lower side of the carrying plate D D is 

 soldered a brass hemispherical shell E E. This shell has a circular 

 aperture on the under side for about a third of its extent. Over- 

 lying the aperture is a thin plate H of corresponding curvature ; and 

 the whole is held together by means of the spring K, and screw L, 

 the latter being tapped into the boss B. The carrier-plate D has a 

 central aperture for the adjustment of the screw, and spring-clips 

 (not shown in the figure) are provided for securing the slide. The dot 

 M indicates the centre of the hemisphere, and should be fully ^^ytli of 

 an inch above the upper surface of the plate D. An object of 

 moderate thickness mounted on an ordinary glass slide will then be 

 approximately in the centre of the movable hemisphere, and will be 

 practically free from displacement, lateral or vertical, in any position 

 of the carrier-phite D D. 



