248 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tained that this invisible part of the solar spectrum extended as far as a 

 wave-length of 5-3 /x. But with the bolometer then in use, delicate 

 though it was, the mapping out would have involved a labour of fifty 

 years. He has since then succeeded in increasing the sensibility of 

 the instrument from the detection of a temperature variation of one- 

 thousandth of a degree Centigrade to that of one hundred-millionth 

 of a degree. He has also connected it with a self-recording photo- 

 graphic apparatus of extreme precision. By these methods he has six 

 series of observations which differ inappreciably from their mean, aud 

 the spectrum is found to contain over 700 lines. 



Tape Measure for Adjustment of Projection Oculars.* — Dr. A. 

 Kohler, in order to minimise the difficulties connected with the adjust- 

 ment of projection eye-pieces, has devised a rearrangement of the scale 

 on the oculars. If the index stands on the zero then the front focus of 

 the projection system lies in the plane of the ocular diaphragm ; if 

 the index is set on another figure then the focus is pushed a correspond- 

 ing number of millimetres behind the diaphragm plane. 



In order to conveniently adjust the ocular head for any desired pro- 

 jection distance (within its due limits) a specially marked tape measure 

 is used. One side of this measure is blue and marked with the figure 

 P 2 ; it is intended for oculars 2 and 3. The other side is red, marked 

 P 4 , and intended for oculars 4 and 6. The tape is divided into divisions 

 corresponding to the graduations on the oculars. In using the tape the 

 operator brings the first graduation into the plane of the screen, mea- 

 sures towards the ocular, and discovers at what interval the plane of the 

 ocular-division will lie ; the figure, found there, gives the number of 

 millimetres by which the ocular head must be screwed out in order to 

 tlirow, at the required distance, an image of the diaphragm on the screen. 



Details are given of the method by which the calculation of the 

 scales on the tape was made. 



Some Evidences of Unscientific Conservatism in the Construction 

 of Microscopes. f — The Rev. G. C. F. Haas, whilst fully admitting the 

 immense improvements of the last half century in the construction of 

 Microscopes, points out that many objectionable features seem to bo 

 retained in various types of instruments simply from the makers' dis- 

 inclination to adopt a change. He thus severely criticises the horse- 

 shoe foot, the want of an inclination joint, small stages, stage-clips, 

 immovable mirror-bars, non-parfocal eye-pieces, &c. There is a Society 

 screw ; why then not one, or at most two, diameters of tube and sub- 

 stage ring? Why have we a dozen or more different tube-lengths 

 instead of one short and one long one ; both measured in the same 

 way ? When shall we have adjustable objectives marked in a rational 

 manner, instead of being engraved with a series of numbers that have 

 no relation whatsoever to thickness of cover-glass or to tube-length, and 

 only serve as a continual puzzle to the memory ? 



Images of Diatom Structure.} — W. Balfour Stokes discusses the 

 •" white dot " and " black dot " images and concludes that Pleurosigma 



* Zeitschr. wiss. Mikr., xviii. (1902) pp. 273-9 (3 fiejs.). 

 t New York Micr. Soc, xv. (1900) pp. 2-6. ■ 

 % Journ. Quek. Micr. Club, 1901, pp. 109-12. 



