580 SUMMARY OF CURRENT RESEARCHES RELATING TO 



with the hour-hand axle of an ordinary alarum clock. This hour-hand, 

 of course, rotates twice per diem, so connexion is made between it 

 and a wheel of twice as many teeth ; but, inasmuch as the rotation 

 is thereby reversed, a third wheel equal to one of the other two is 

 required. It is necessary that the hypotenuse should lie due north 

 and south. 



Polariscope and Microscope Lantern.* — The following details 

 will enable any one to make a polariscope for the lantern. Make first 

 a tube of tin or brass, about 4 in. diameter, to fit the tube of the 

 lantern, and at an angle of 56° 45' fix a similar tube 4 in. long. Part 

 of the elbow is cut away to introduce a bundle of 10 or 12 plates, 

 4^ in. by 34; in. of thin patent plate-glass. The lowermost of these is 

 blackened. A hole for stage, 2 in. by lh in., is cut on each side of this 

 tube, and a plate is fixed in tube here with a 2-in. hole in centre. This 

 forms the stage. A sliding tube with a similar plate at end, and a 

 spiral spring serves to keep objects in position. At the end of tube fix 

 a flange and another short tube about 3 in. diameter, which carries the 

 objective, — of about 4-in. focus. The objective moves in this tube with 

 a sliding or rack-and-pinion movement. Beyond this again is still 

 another tube 2 in. diameter and 2 in. long. In this slides a smaller 

 tube, in which is fitted a Nicol prism. This fits in a cork, which cork 

 fits in small tube, and the smaller tube rotates in the other. 



Lantern Microscope. Get a brass tube 3 in. long and 2 in. diameter, 

 and at one end fix a screw, fitting flange of the lantern. Two inches 

 from this end cut holes on either side, 2 in. by 1J in., and fit for stage 

 as in the polariscope. At about 1^ in. from end is fitted a lens about 

 2^-in. focus, which acts as an additional condenser. To the other end 

 of the tube fix a plate, in centre of which fix a tube 1 in. diameter 

 and lj in. long. In this slides a smaller tube carrying the magnifying 

 lenses, which may be two lenses each about 2-in. to 3-in. focus. If 

 these are not achromatic a diaphragm with \-m. hole must be placed 

 about f in. in front. The best position is determined by experiment. 

 Achromatic lenses will be best. Micro-objectives of 1-in., l^-in., or 

 2-in. focus may be utilised with advantage by fitting them by means 

 of a cork in the sliding tube in place of those mentioned. Instead of 

 a sliding tube a rack-and-pinion will be a great advantage. 



(4) Photomicrography. 



Microphotographs.t — The production of these small views, or 

 microphotoijraphs, is a branch of work which requires very considerable 

 patience and skill, inasmuch as it is necessary to perform the operations 

 of development, etc., in the field of a magnifier or small Microscope, 

 since the size of the image is so minute. The majority of the micro- 

 photographs sold are made on the Continent, and details of their rnanu- 



* Photographic Reference Book, 2nd ed., 1904, p. 23S. 

 t Tom. cit,, pp. 191-2. 



