OF ANIMALCULES. 21 



that of Dr. Goring), which is easily arranged to shew 

 these creatures and their domestic habits in the phials 

 they are kept, adhering, as many of them will, to its 

 sides. Although no English work on this subject has 

 previously given any admeasurement of the sizes of the 

 different species, yet as 1 conceive it to be a matter of 

 some importance, I shall point out the method I have 

 pursued in accomplishing it. Thus; a system of gradu- 

 ation is easily formed on the aquatic live-boxes, or slips 

 of glass, by means of cross-lines intersecting each other 

 at right angles ; and under a series of these lines, say 

 1 -500th of an inch apart, an animalcule may be so exa- 

 mined as to afford a very accurate estimate of its dimen- 

 sions : for instance, suppose it to occupy one-half the in- 

 terval between two of these lines, then it is clear that the 

 creature measures 1 -1000th of an inch : and if it occupy 

 two divisions, compute it at ] -250th of an inch in length. 

 In this manner, with a little practice, and with the aid 

 of a few micrometers of different grades, the intention 

 will be readily effected. 



Having selected and placed the object for examina- 

 tion on the stage of your microscope, the next conside- 

 ration will be how to regulate the illumination, and to 

 select a suitable magnifying power. These points must 

 be carefully attended to, for on them, even with the best 

 instruments, much of the beauty and effect will depend. 

 The most intense and best description of light is to be 

 derived from either a sperm or wax candle, or from what 



