194 Dr. A. E. H. Tutton. The Masmometer, a New [May 12 



blocks, which are adjustable as to their distance apart, and are suitably 

 recessed at their inner ends to accommodate the wedges and the plate- 

 supporting and weight-applying apparatus. They slide on a very rigid 

 larger block of steel, mounted to the front and left of the centre of the 

 iron base, and one of them is provided with fine adjustments for altitude 

 and azimuth, to enable the knife-edges to be set exactly parallel. 



(2.) A pair of mechanical " fingers," for supporting the plate and 

 adjusting it in the proper position under the knife-edges, and for 

 eventually pressing it up into just full contact with the latter. They 

 are carried by a fitting to the left side of the steel block, and terminate 

 in little spring tables each carrying a small gunmetal knife-edge above 

 its inner side. They are adjustable for separation, height, and their 

 position in or out of the recess. 



(3.) A delicate balance, by Oertling, of special construction, at one 

 end of whose beam the bending weight is applied through an upright 

 agate point, the pressure-point, which is carried instead of a pan at this 

 end. The balance is mounted to the right of the steel block on a strong 

 base, which is movable by rack and pinion so that the pressure-point 

 can be exactly centred under the plate, and a fine adjustment for 

 azimuth is also provided in the mounting of the balance to aid in this 

 object. A pan at the right-hand end of the beam receives the bending 

 weight, which may amount to 500 grams., and a counterpoise for the 

 weight of the pan is provided near the left end. 



(4.) A transmitter, for conveying the bending movement of the 

 centre of the plate to the interference apparatus. It takes the form of 

 a T-piece, whose long stem is horizontal and is fitted with an agate 

 wedge, by which it rests on an agate plate carried on the front block, 

 and a counterpoise ; the lower end of the vertical crosspiece rests with 

 less than 1 gram, of pressure on the centre of the plate, while its 

 upper end terminates in a black glass disc, which is adjustable above 

 a metallic one so as to bring its polished surface truly horizontal. 

 This surface is the lower one of the two which reflect the interfering 

 light. 



(5.) An interference tripod for supporting the large colourless glass 

 disc whose under surface forms the upper of the two surfaces concerned 

 in the interference. One screw is mounted on the back block, and 

 two screws are carried on the front block ; the stem of the transmitter 

 passes between these latter, and the black glass surface is only separated 

 from the colourless disc by a film of air of the necessary thickness to 

 allow for its diminution, consequent on the bending of the plate, without 

 contact of the surfaces. 



(6.) A measuring microscope, wherewith to determine the dimensions 

 of the plate and to find its centre. It is mounted to the left of the 

 steel block, and its two rectangular measuring movements read to 

 a thousandth of a millimetre by a novel direct method, involving the 



