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spectrum, all of which may be source* of error with careless observers, 

 and which, if they apply to my method, apply with, perhaps, more force 

 (as I could show) to that usually pursued by indirect light, especially that 

 of the lamp, so much recommended, though it is wholly useless, for the 

 purposes of minute and exact observation. The method I have pursued, 

 whether good or bad, is not followed. It is sufficient to mention the 

 opinions of two of the most eminent, recent writers on this subject : Sir 

 David Brewster says, (Ed. Ency.) " Microscopic objects are commonly 

 seen better in ramlle light than in day light, a fact which is ■particularly 

 apparent vhen very high magnifying powers are employed ; and we have 

 often tbmid that very minute oljjects, which could scarcely be seen at all 

 in day light, appeared with tolerable distinctness by candle light. So 

 far as we know, the cause of this has not been investigated." Now, 

 this is very plain to myself. In a good light, that is, in the direct rays 

 of the sun, a focal point never can arise from an entire vessel or organ 

 of any animal, even including those called the infusoria, but only from 

 some portion or molecule of such vessel or organ. Hence, all struc- 

 tures as nerves, muscles, heart, &c., are, in a certain sense, annihilated, 

 or become, as it were, structureless. This gentleman gives a list oi what 

 he calls microscopic objects^ which he recommends, without indicating 

 any preparation, as most suitable for examination, among which are the 

 spider, bug, mole-cricket, glow-worm, leech, corals, sponges ! Now, 

 the true focal point for one hair of the glow-worm, will be extremely 

 limited for that part, but cannot answer for another hair, much less for 

 the animal's entire body, which, were it sufficiently pellucid, w^ould pre- 

 sent an indefinite, nay, almost infinite number of focal points. Dr. L. 

 Mandl, lays it down as a microscopic axiom, to avoid the direct light of 

 the sun, chiefly because it produces irisaiion ! (iMandl et EHRE^"BERG, 

 Traite du Microscope). Dr. M. admits that a lamp has the same effect. 

 I am unable to see any thing in his statements which justifies him in his 

 love for a dim, and his dread of a bright light. 



When the observations are properly conducted, the calorific rays, 

 combined with the solar spectrum, including desiccation and certain 

 molecular movements incidental to the same, so far from vitiating, really 

 aid the experimental operations. The proper management of the light 

 is the fundamental point. It is not in the sjjectrum, but upon its margins 

 or boundaries where tlie eye must be fixed, in order to avoid the dazzling 

 and other bad effects of a concentrated light. 



Omitting all matters which are not essential to the intimate structure 

 of animal and vegetable microscopic objects, as color and the like, three 

 distinct things are seen in the direct solar light, and which I must explain, 

 as they have no reference whatever to the terms used by others : 



First, Infusoria : these animals have no resemblance to any of those 

 called or described by the same name, or represented pictorially by 

 Mandl, Ehrcnberg, and others, and which have been arranged by Miiller 

 into 2 classes, 17 genera, and 37? species. I may call them solar 

 infusoria, because seen in sun only. They are filiform, cylindrical, 

 lead colored : all are exactly alike. They endure boiling and all degrees 

 of heat short of incineration, and remain desiccated for indefinite periods, 

 and may be triturated without destroying their vitality, that is, their 

 power of motion. They always move in both dead and living matter, 



