358 



We will now pass on to 1886, the date of the introduction of 

 the apochromatie objective, all the old difficulties and im- 

 possibilities were at once dispelled, and anyone who took the 

 smallest interest in the matter could see that there was a 

 glorious future for photomicrography. My apparatus was once 

 more set up, and without difficulty results were obtained which 

 surpassed the most sanguine expectations of former years.* 

 However, it was not long before it became evident that number 

 2 apparatus was, as hinted above, unsuitable for the work. It 

 was, therefore, condemned, and number 3, which is now 

 before you, was designed. 



You will at once see that in its broad outline it is a combina- 

 tion of the first and second, inasmuch as the board and the 

 trestles are both retained. The trestles are both alike, and 

 of the common tripod form, the board is of teak, very massive, 

 being 8ft. by 1ft. ; the upper surface is perfectly smooth, but 

 not polished. 



The feet of the trestles rest on blocks of cork, and slabs of 

 cork are placed between the board and the trestles. From 

 each table between the legs of the trestles hangs half a cwt., 

 and underneath the board hang four quarter cwts. This weight 

 gives great stability to the whole apparatus. A bolt passes 

 through the board and the top of the trestle — this should not 

 be screwed up, but left quite loose. The height of the top of 

 the board above the ground is 4ft. ^in. ; this has been adjusted 

 to my own height of 5ft. lOin. 



Nothing except the focussing rod passing down one side of 

 the board, with its corresponding pulley on the other side, is 

 fixed to the board. 



We now come to a distinct difference between this and the 

 former designs, viz., the presence of a camera. By camera is 

 meant the dark chamber which connects the eye-piece of the 

 microscope to the dark slide, for this camera is not at all like 

 any ordinary camera, because the bellow^s are replaced by 

 rectangular mahogany tubes (6| X 5| outside measure), capable 

 of being joined up in any order. There are also two troughs, 

 each 3ft. long, made of mahogany, stoutly built and heavy, 

 resting on three points ; these are for the purpose of carry- 

 ing the tubes. The tubes are, however, perfectly free from 



* See this Journal, Ser. 2, Vol. iii., 1 1. 18. 



