APPENDIX. 297 



diameters with a sufficiently strong light.* It is necessary 

 that the instrument should be solidly mounted, and should 

 admit of being easily worked. The more simple it is, 

 the less space will it occupy, and consequently it will be 

 the more readily adapted to the requirements of the ob- 

 server. Some of the arrangements adopted in our day 

 seem to be so perfect as to leave nothing to be desired, f 



NOTE IV. 



M. Milne Edwards, who is a member of the Institute 

 (Academy of Sciences), Professor at the Jardin des 

 Plantes, and in the Faculty of Sciences of Paris, is 

 incontestably one of the leaders of zoology in its present 

 state. His labours, which are as important as they are 

 numerous, have justly secured to him the high position 

 which he holds, whilst his elementary works have 

 rendered his name universally popular. M. Milne Ed- 

 wards, at an early age, made the Invertebrata the 

 objects of his scientific research, and he soon understood 

 that in order distinctly to comprehend the history 

 of these animals, it was necessary to study them in their 

 native habitats. In association with his friend and fellow- 

 labourer, M. Audouin, he was the first to set the ex- 

 ample of those prolonged sojourns on the sea coast which 

 are alone able to afford opportunities for the serious 



* A magnifying power of a thousand diameters will enlarge the 

 surface of the object 1,000,000 times. It will be readily understood 

 that the clearness of the images must of necessity diminish in 

 proportion to the height of the magnifying power, since the same 

 quantity of light has here to form a much larger image. 



f See for farther details, M. Dujardin's Manual, and the work 

 of M. C. Chevalier, to which we are indebted for the principal 

 historical details already given. This treatise is entitled, Des 

 Microscopes et de leur -usage. [We may refer our English readers to 

 Quekett's Practical Treatise on the use of the Microscope.] 



