194 NOTES AND MEMORANDA. 



not disclosed, and several ineifectual attempts were made to reproduce 



them. The following is stated to be the method of manufacture : * — 

 A solution of chloride of gold and ammonium 

 is placed in a shallow dish coated with heavy gold 

 foil, which is connected with the zinc plate of a 

 large Daiiiell's battery. Near the top of the solu- 

 tion, and connected with the copper plate of the 

 battery, a roll, made up of thin strips of pure gold, 

 is susj^ended, enclosed in a muslin bag. The 

 strength of tho battery current is controlled by a 

 »» coil of wire arranged as a rheostat, a clamp ter- 

 minating one of the battery wires enabling the 

 operator to include a greater or less number of 

 coils in the circuit. The necessary conditions 

 being fulfilled, on completing the circuit the gold 

 is gradually dissolved from the roll and deposited 

 on the bottom of the dish in bright crystalline 



flakes, having the appearance of feathers or fern-leaves when examined 



under the Microscope. 



The Vertical Illuminator. — This illuminator was originally in- 

 tended to be used in conjunction with medium-power dry objectives, 

 of moderate angles, such as were formerly so much in vogue. Mr. 

 Morehouse, a well-known microscopist of Wayland, New York, has 

 found that by the conjoint use of the illuminator with immersion 

 objectives of high balsam apertures, astonishing results may be 

 secured ; as, for instance, the resolution of the markings of Podura 

 and other insect scales, the striation of valves of Frustulia Saxonica, 

 Surirella gemma, and similar " difficult " diatoms, under amplifications 

 of 3000 and 4000 diameters, and, as a matter of course, by reflected 

 light. 



Dr. Edward Smith has devised a modification,! consisting of an 

 adjustable shutter, regulating the admission of light, thus greatly 

 improving the brilliancy of the objects, accompanied Avith marked 

 increase of resolving power ; and with the instrument thus modi- 

 fied he had no difficulty in obtaining beautiful displays of the 

 Nobert 19th band, the simultaneous exhibition of the long and trans- 

 verse strife of Frustulia Saxonica, &c., under powers of 3000 ^nd 

 4000 diameters. 



Desiring to test it on histological preparations, he thus examined 

 a slide of human blood, improvised for the occasion, and was asto- 

 nished to find about three-fourths of the red corjjuscles nucleated. 

 The amplification employed in these observations was about 3700 

 diameters. 



A point which should not be lost sight of is that the vertical 

 illuminator can only be successfully used in conjunction with an 

 objective of high balsam angle. 



* Mr. A. H. Chester, in 'Amer. Journ. of Sci. ami Arts,' 3rd ser., vol. xvi. 

 (1878) p. 29. 



t 'American Naturalist,' vol. xiii. (1879) p. 137. 



