50 SIMPLE MICROSCOPES. 



with the aspect of Urinary deposits, may, by this little instrument 

 (which he can carry in his waistcoat-pocket), discriminate on the 

 spot the nature of almost any sediment whose character he may 

 wish to know, without being obliged to have recourse to a more 

 elaborate apparatus.* 



36. Field's Simple Microscope. — The general purposes of a 

 Simple Microscope are satisfactorily answered by the instrument 

 which gained the premium some years ago awarded by the Council 

 of the Society of Arts, and which is capable of being very effectively 

 used in the examination of most of the objects for which such an 

 instrument is suited. It consists (Fig. 28) of a tubular Stem, about 

 five inches high, the lower end of which screws firmly into the lid 

 of the box wherein the instrument is packed when not in use. To 

 the upper end of this stem the Stage is firmly fixed ; while the 

 lower end carries a concave Mirror. Within the tubular stem is 

 a round pillar, having a rack cut into it, against which a pinion 

 works that is turned by a milled-head ; and the upper part of this 

 pillar carries a horizontal arm which bears the lenses, so that by 

 turning the milled-head, the arm maybe raised or lowered, and the 

 requisite focal adjustment obtained. Three magnifiers are supplied 

 with this instrument ; and by using them either separately or in 

 combination (the lens of shortest focus being placed at the bottom, 

 whenever two, or all three, are used together), a considerable range 

 of powers, from about five to forty diameters, is obtained. The 

 Stage is perforated with holes at its four corners, into either of 

 which may be fitted a Condensing lens for opaque objects (§ 90), or 

 a pair of Stage-Forceps (§ 94). An Aquatic Box for the examination 

 of objects in water (§ 97) is also supplied.f This instrument is 

 peculiarly adapted for Educational purposes ; being fitted in every 

 particular for the examination of Botanical specimens, small Insects 

 or parts of insects, Water-fleas, the larger Animalcules, and other 

 such objects as young people may readily collect and examine for 

 themselves : and those who have trained themselves in the appli- 

 cation of it to the study of Nature, are well prepared for the advan- 

 tageous use of the Compound Microscope. But it also affords to 

 the Scientific inquirer all that is essential to the pursuit of such 

 investigations as are best followed out by the concurrent employ- 



* This Microscope, the invention of Prof. Wm, Gairdner of Glasgow, is 

 made by Mr. Bryson, Optician, of Edinburgh. — A modification of it, to be 

 specially used as a " Diatom-Finder," has been described by Mr. Tomkins 

 in the " Trans, of the Micr. Soc." N.S. (1859), Vol. vii. p. 57. The general 

 arrangement of Dr. Gairdner's Microscope is adopted ; but the Doublet 

 is replaced by a ' Coddington ' lens of 5-8ths-inch focus, which (accord- 

 ing to Mr. Tomkins) suffices for the detection of all the ordinary forms 

 of Diatomacece, and an Aquatic Box is substituted for the brass ring and 

 the disks it carries. 



t The price of the instrument, with all these appurtenances, packed in 

 a neat mahogany box, is only half-a-guinea ; and the maker, Mr. G. 

 Field, of Birmingham, is bound by his agreement with the Society of 

 Arts to keep it always in stock. 



