718 SUMMARY OF CURRENT RESEARCHES RELATING TO 



model A. The instrument can be applied to a large object, either 

 directly or by help of a laboratory stand, exactly as A. 



2. Measuring Microscope for Negatives. — -This (plate XX. fig. 3) is, 

 in the first instance, intended for the measurement of photographs of 

 physical observations, e.g. spectra. It has the same ranges of movement 

 and accuracy as models A and B. It may also be used for exploring 

 plates of 6 by 9 cm., and for many other purposes. It differs from the 

 previous instruments in possessing a stable understage with illuminating 

 mirror, and a strong stage with central aperture of about 3 cm. diameter. 

 But it resembles them in being provided with the collar H, and similar 

 overstage. It has the same facilities for adaptation to a laboratory 

 stand. The square strong stage is so worked on its right and left side 

 planes that these can serve as guides to a metal frame sliding on the 

 stage top. On this frame the plate to be measured is secured with two 

 springs ; the plate is then pushed on to the millimetre divisions serving 

 as a bed. The frame can thus be pushed perpendicularly to the direction 

 of the slide-guides and clamped by the screw N. Comparison of equal 

 intervals of spectra is attained by this movement of the frame. 

 Besides these millimetre graduations, there is also a second series, 

 perpendicular to the first and readable through a window pierced in the 

 frame. The two series serve as co-ordinates for localising any spot on 

 the plate. 



3. Capillary Measuring Microscopes. — These are made in two models 

 (D, E), and have been suggested by the firm of F. A. Kiihnlenz. They 

 are intended for direct reading of the internal diameters of capillary 

 tubes of any length, and therefore facilitate the rapid sorting of large 

 quantities of such tubes according to their bore. The Microscope is 

 adjustable with rack-and-pinion T, and has a magnification of about 

 100 diameters. The ocular contains a scale (plate XXI. fig. 5) reading 

 the object to the hundredth part of a millimetre. Plate XXI. fig. 4 

 shows model D, about half full size. The capillary tubes, which may 

 be 1^ metres long, are placed on the board B, and the operator com- 

 mences to read the lowest layer. As the Microscope is more easily 

 moved than the heavy tubes, the instrument is placed on a slide which 

 traverses the row by means of the hand-wheel R. In this way every 

 tube of the lowermost layer can be successively brought into the field 

 of view of the Microscope. Plate XXI. fig. 5 shows the appearance 

 presented in the ocular. It is found convenient to take first the 

 higher reading (28 in this case) and then the lower, as the figures are 

 then conveniently placed for subtraction. It would, of course, be 

 possible to place one edge of the circumference on the zero and take 

 the diameter by direct reading ; but experience shows this to be a slower 

 way. By means of the screw S, the board is lowered till the next layer 

 of tubes comes into view. These are tested in similar fashion. The 

 instrument may also be used for calibrating thermometer tubes. In 

 that case the spindle carries a micrometer screw, and the hand-wheel 

 has a micrometer drum divided into 100 parts. 



Model E, seen in plate XXI. fig. 6, consists of a Microscope with 

 rack-and-pinion. It has the same optical equipment as model D, but is 

 mounted on a pillar of adjustable height. It may be used for the tubes, 



