March. 1912. 



kxo\vli:dge. 



I'lGLRIi 114. 



Holders. — The nature of the object 

 holder will necessarily vary with the nature 

 and size of the object. 1 ijive two very 

 generally useful forms. Fissure 112 shows 

 us a small rather hea\y box to which 

 are fixed two thin flat pieces of wood 

 leg., bits of cigar box lid). To these, in 

 turn, are screwed two ordinary wood 

 spring (.American) clothes clips, which one 

 may get by the dozen for a few pence 

 at any " oil shop." This contrivance en 

 ables us to hold any ordinary microscopi<- 

 slide, as shown in Figure 112. 



F'igure 113 is a similar hea\y box used a> 

 a base ; to this a pair of spring clips are 

 fixed. These, in turn, grasp a pair of 

 clean thin glass plates between which it is 

 often convenient to " sandwich " such a 

 thing as the flowering part of Poa ainiiut. 

 and so on. 



Passing now to photographic arrange- 

 ments, we have in Figure 114 one of the 

 simplest contrivances imaginable — viz.. a 

 flat, straight, thick, heaxy piece of wood, 

 which serves as a baseboard on which rests \, an ordinary 

 camera, with extension lens tube B, which requires a support 

 C (shown in a subsequent figure, E 120). The object sand- 

 wiched between two pieces of plain glass is held at E (in 

 the contrivances shown in Figure 113). At R is a small 

 circular mirror fitted up for use as a reflector, also shown 

 in other figures. 



Some such simple contrivance as this may serve the care- 

 ful and patient worker for occasional use, but it will be found 

 that there is considerable risk of getting the parts out of 

 position unless we have some read.\- means of fixing them to 

 the baseboard. In connection with the plan of using a glass 

 sandwich arrangement. Figures 113 and 114, it should be noted 

 that there is in certain lightings a considerable risk of getting 

 harmful reflections. To obviate this the following plan is 

 efficient. To a piece of stout card (c.^*.. straw board) fix a piece 

 of rough black cloth by means of paste oi glue. This card may 

 be about eight by six inches'. \Vhen the paste is dry, cut a 

 circular hole the exact size of the glass part of the lens, and 

 in such a position that when the card rests on the baseboard 

 this hole just coincides in position with the lens opening. 



FiGURi: 11. i. 



Such an anti-reflection contrivance is shown in working 

 position, /.e., close up to the face of the lens, in Figure 114. 



I now pass on to a \'ery much more useful form of base- 

 board. This, in my case, consists of a piece of teak about 

 four feet long, two and a-half inches wide, and half an inch thick. 

 This is firmly fixed by means of an ordinary camera screw 

 (A, Figure 1161. which loosely fits the central hole of the tripod 

 top, but its thread engages with the wood of the baseboard. 

 •The camera is fi.xed to the baseboard by a second similar 

 screw, B. The object is held in a holder, D, to be presently 

 described, while E is a mirror reflector. At C is shown a 

 piece of card covered with black cloth. This is used for 

 making the exposures. It is here shown to be leaning up 

 against the objective, which in this case is conjoined with the 

 Davis diaphragm. The advantages of this system are porta- 

 bility. I.e.. we can move the whole thing about together so as 

 to get the object in a favourable lighting, and it is remarkably 

 free from the efl"ects of vibration, any disturbance of the floor 

 causing the whole contrivance to vibrate as one thing. 



Next a word as to the object holder. The general arrange- 

 ment will be made sufliciently clear by a glance at F"igures 

 1 15 and 117. The former .shows that this apparatus is made 

 to slide along and yet grip the baseboard along its edges. 

 Figure 1 1 7 shows how the two holding springs are fashioned out 

 of pieces of an ordinary steel knitting needle. This is made 

 red hot in a gas flame and then gently bent to the shape shown 

 by the aid of a couple of pairs of pliers. When piercing the 

 sight hole in the holder (Figure 115) it is important that its 

 centre is just opposite the centre of the lens extension tube. 

 This will be found of help when getting 

 the object slip into position, and also in 

 getting the axis of the camera parallel to 

 the baseboard. 



In Figure 118 we see a back view of the 

 mirror and its mount. The mirror is about 

 four inches in diameter, and has a thin 

 metal rim-frame. .\ semi-circular hole is 

 cut out of the thin flat piece of wood A 

 and the mirror swung by two screws C, C — 

 just tight enough to hold it at any desired 

 angle. At B a small block of wood is 

 .added to give weight and firmness and 

 prevent the whole thing being top-heavy. 

 In Figure 119 we see the front side of the 

 mirror holder and should note carefully a 

 small circular peg or dowel in the front 

 edge of the holder. This engages with an 

 easy fitting hole in the baseboard and 

 enables the holder to be turned about a 

 vertical axis through this dowel or peg, 

 while the two side screws C, C give us a 

 horizontal axis ; thus we can set the 

 mirror at any angle by combining these 

 two movements. 



I now come to the last bit of home-made 



FlGUKt 110. 



