150 ANNUAL OF SCIENTIFIC DISCOVERY. 



ond, had precisely the same source of light been employed; never- 

 theless, in spite of this disadvantage, to which they were purposely 

 exposed, the magnesium and electric pictures are far superior to 

 that taken by sunlight, and of the two the electric is the best. It 

 is especially to be observed that in the electric picture the contrast 

 obtained is so great that the objects appear clearly defined on an 

 almost perfectly white ground, which is never the case Avith 

 photo-micrographs taken with the sun as a source of illumina- 

 tion." 



The second report concerns the use of the lime-light for photo- 

 micrograpbic purposes. Pictures have been successfully taken 

 with powers as high as 1,000 diameters. The practicability of the 

 use of this light islmportant, because of its cheapness, its greater 

 steadiness, and the little trouble given in its management. In 

 his experiments Col. W. made the hydrogen as he consumed it, 

 and sometimes made the oxygen in the ordinary manner, some- 

 times purchased it compressed in iron cylinders. The lamp used 

 was a large magic-lantern burner. The magnifying lenses being 

 removed, a cone of light proceeding from the condenser of the 

 lantern was allowed to fall upon the achromatic condenser of the 

 microscope as with the magnesium lamp in the earlier series of 

 experiments. The ammonio-sulphate cell was used, but the 

 ground glass required with the electric light was unnecessary. 



The time of exposure required was much the same as with the 

 magnesium lamp, and the pictures are equally good, for though 

 the actinic power of the naked lime light is less than that of the 

 magnesium light, the question of steadiness, involving the possi- 

 bility of great concentration, plays a very important part. 



The lime light had never before been successfully employed 

 thus in this country, though some successful attempts were made 

 several years ago in England, by a less perfect process than the 

 one used by Col. Woodward. Experiments have been made in 

 England by Messrs. Maddox, Abercrombie, and Wilson on the 

 use of the magnesium light, but no results were obtained compar- 

 able with those described in the report. 



Besides photographs of the sixth square of a Holler's Diatom 

 Plate by solar, electric, magnesium, and calcium light, Col. W. 

 presents several other photo-micrographs illustrating the perfec- 

 tion of the process. Photographed by the magnesium light the 

 diatom Aracliinoidiscus Ehrenbergii, magnified 400 diameters by 

 a Wales' one-eighth objective, shows the elegant radiation and 

 form of the dots with perfect clearness. A second example by 

 this light is a nitrate-of-silver injection of a small vein and 

 capillaries in the muscular coating of the urinary bladder of the 

 frog, also magnified 400 diameters. Four photo-micrographs of 

 diatoms by the electric light, magnified from 340 to 2500 

 diameters, show the markings very finely, as does also the admi- 

 rable photograph of Navicula lyra taken by the lime light. Inter- 

 esting as showing the perfect success attained in the original 

 design of the experiments are photographs of an epithelial 

 cancer of the larynx, magnified 400 diameters by Wales' one- 



