46 TRANSACTIONS AND PlIOCEEDINGS OF THE [Sess.'lxi. 



FIRST METHOD. 



Apparatus. — That I have used is the photo-micrographic 

 apparatus by lieichert, of Wien. It has the advantage that 

 it can be used either vertically or horizontally, the change 

 of position being accomplished in a fraction of a second. 

 This is a real advantage, because one requires to vary the 

 position of the camera when dealing with specimens where 

 particular manipulation of the light is necessary to get the 

 best results. (3u a table at one side of the apparatus, I 

 have had fitted a Welsbach Incandescent Gas Light 

 installation with a bye-pass. This I use for focusing, and 

 find it much to be preferred to an Argand or a petroleum 

 lamp, on account of the character and intensity of the light. 

 It may not be amiss to advise the use of the apparatus 

 without a funnel, which is continually in the way, and, in 

 the case of rupturing of the mantle, entails nasty accidents. 

 The Welsbach is fitted with a stand and clamp, so that it can 

 be moved about in any direction, and put at any height 

 that may be necessary. On the opposite side of the 

 camera is fitted the radiant. This consists of a magnesium 

 ribbon apparatus, arranged like the AVelsbach, to permit of 

 every freedom for moving as desired, either horizontally or 

 vertically. 



Having removed the microscope and all the microscope 

 fittings from the camera, I affix, by means of an adapter, 

 a half-plate photographic lens with iris-diaphragm into the 

 front aperture of the camera, where the light -excluding 

 capsule of the microscope tube usually slides. 



This lens has a diameter of a little over 30 millimetres, 

 and, when the wood surface is at a distance of about twelve 

 inches from the iris, gives a distinct micrograph, under low 

 magnification, of a surface of at least three inches on the 

 focusing-screen, at a distance of twenty-si.K or so inches' 

 from the iris. 



ruELiMiNARiES. — A typical piece of the dressed wood 

 surface is selected, and a series of measurements made to 

 enable the operator to fix the block so that the desired field 

 may be covered by the lens. The log is now securely 

 propped up in position at the necessary distance in front 

 of the leris ; and it is important that it be fixed so as to be 

 perfectly immovaljle, in order that the surface may be and 



