236 MEMORANDA. 



more, whether the DiatomaceaP are properly classed in the 

 vegetable kingdom ? 



I would take this opportunity of impressing upon the atten- 

 tion of those microscopists, who wish to examine for them- 

 selves the ciliary movements of the lower forms of life, the 

 necessity of using only very shallow cells for the purpose, say 

 of from l-50th to 1-lOOth of an inch deep, and glass covers of 

 from 1-1 50th to l-250th of an inch thick. The objective 

 must be l-4th or l-8th, with a good eye-piece; the objects 

 themselves should be carefully illuminated, by using for the 

 purpose a parabolic reflector, or a Gillett's condenser, and the 

 examination be conducted during very bright weather or in 

 sunlight. — J. Hogg. 



New Mode of lUuiuiimtion. — Your obliging insertion in the 

 last number of the ' Microscopical Journal,' of my note on 

 ' Closterium,'* tempts me to send you another Memorandum, 

 in the hope it may be found worthy of a similar corner in 

 your next. 



Those who, like myself, do not happen to possess either a 

 Wenham's or Shadbolt's parabolic condenser, will find the 

 following plan an efficient substitute, perhaps even superior 

 to those instruments for defining certain structures. 



With a steady clear lamp-light throw a strong background 

 illumination, according to the method of the Rev. Mr. Reade, 

 rendered more intense by using a bull's-eye lens placed near, 

 and with its convexity toward the light, and a smaller con- 

 densing lens (on a separate stand), focusing the bright light 

 on the object beneath the stage, and at an angle beyond the 

 range of the angular aperture of the objective. Then let the 

 rays which have passed througli the slide be received above 

 the stage, on either a side-reflector or a Lieberkuhn, placed 

 so as to reflect them on the ol^ject from the side opposite 

 to the light. A brilliant illumination on a dark or black 

 ground is thus produced, which displays many objects with 

 extr<"me distinctness and beauty, and, as in all background 

 illumination, with the great advantage of preserving their 

 natural form and colour. 



Among those best adapted for illustration by this method, 

 are the coloured spiculse of Gorgonia ; recent and fossil 

 Foramwifera ; partially-transparent injected preparations ; 

 palate of Myliohates ; hair of Indian Bat ; scales of Lepisma, 

 of Amathusia Horsfeldii, and of many other butterflies and 



* Allow me to correct a mistake of your printer, in inserting the last 

 liaragraph but two at page 172, which was not intended for the j^ress, but 

 to account for the erasure of some experiments narrated in the original MS. 



