THE president's ADDRESS. 357 



form, though in the main it followed that of Dr. Woodward ; as 

 it has long since been broken up, you will not be wearied with 

 a description ; it need only be said that the work was carried on 

 in the dark room, there being no camera of any description. For 

 simplicity and ease of adjustment, this method of Dr. Wood- 

 ward's has no rival, nevertheless, as is the case with all good 

 things, there is a " but," which is, but you require one if not 

 two rooms devoted to it, and to nothing else, conditions which 

 are not always obtainable. Suffice it to say that after some 

 work, not one, but a whole comedy of errors was found in the de- 

 sign, so it was broken np and another made. The second differed 

 from the first, inasmuch as the microscope and the plate holder 

 were supported, not on separate trestles, as in the first, but on a 

 plank which rested on a table. Paraffin now took the place of 

 oxy-hydrogen, and like it was enclosed in a dark lantern, no 

 camera being used. Work performed Avith this apjDaratus 

 showed me that in some respects it was better than its prede- 

 cessor, and in some respects not so good. 



The photographic part of the work, though crude in the 

 extreme, for at that time I had never done any ordinary 

 photography, was improving, but all my negatives, taken with 

 high powers and large axial cones of light, were failuies. 

 However, with low powers, and medium jDOwers with small 

 cones of illumination, and high powers with oblique light 

 striae resolutions, better success was obtained. The great 

 difficulty, which could not be overcome, was an indistinct- 

 ness of image sufficient to blot out all detail when large cones 

 of illumination were employed. Displacements of foci, correctors 

 at the back of the objective, ammonio-copper cell, were tried 

 in vain ; the details, which with the microscope were visible 

 to the eye, were still invisible on the jDlate, and so I gave up 

 photomicrography. Fair pictures of the A. pellucida, and of 

 the old exclamation marks on the Podura scale, were obtained, 

 but anything like secondary structure, or fractures through 

 secondaries, were blotted out. The isochromatic princij^le, if 

 discovered at that time, was quite unknown to me. Perhaps 

 further work might have secured better results, and, photo- 

 graphically speaking, it would have undoubtedly done so, but 

 not until it was proved that the main error lay in the objective 

 was the work given up. 



