1883.] 



MICROSCOPICAL JOURNAL. 



Some time after the completion of 

 the formula of this ^V> t^^Y ^^'^'''^ ^^' 

 quested by me to make a new homo- 

 geneous ^ in., which resolving power 

 should be held paramount, and which 

 should excel both the new -^j, and 

 their i of 120° b. a. The new I would, 

 of course, necessitate a new formula, 

 and that of the ^'^ was modified and 

 adapted to the power of the ^. 



The Spencers assured me that this 

 I was positively the best objective they 

 had ever looked through, and as a few 

 words concerning it may be of interest, 

 I will describe it. 



The mounting is similar to that of 

 the old I, of red brass and gracefully 

 proportioned. By means of a gradu- 

 ated screw collar, a rectilinear motion 

 is given to the back systems sufhcient 

 to bring about the proper correction 

 for use with water, glycerine, or ho- 

 mogeneous fluid, or for a considerable 

 length of draw tube. The magnifying 

 power — measured at ten inches from 

 the front lens — is, at the open point, 

 63, at the closed point 70 diameters. 

 The angular aperture is given as 130° 

 in balsam, and is constart throughout 

 the entire range of the collar — if the 

 same fluid be used. The residual col- 

 or is somewhat greater than is usually 

 seen in Spencer's objective ; but still it 

 is well corrected, and the field is flat. 

 This objective is remarkably sensi- 

 tive as regards spherical aberration, 

 and a slight change in length of body, 

 or so called homogeneous fluid, makes 

 itself known by a disturbance of the 

 spherical correction. 



The special quality desired — that 

 of resolution — is not disappointing. 

 The diatoms of MoUer's balsam plate 

 are easily resolved — No. 16 in dots 

 by central light, and No. 18 in dots 

 by oblique light — lamplight. 



Accepting the orthodox view, it 

 would seem unreasonable to expect 

 such an objective to do well on histolog- 

 ical work, but, on the contrary, it works 

 beautifully. The circulation of blood 

 in a frog's foot is beautifully shown 

 with this glass — using it, of course, as 

 a water-immersion, without covering 



glass, and with powers as high as 

 1,000 diameters. The white corpuscles 

 can be seen much better than with any 

 narrow angled glass with which I am 

 acquainted. I regard a frog's foot as 

 a very good histological test- The 

 circulation of blood and contraction of 

 the muscles in the leg of Ranatra fusca, 

 are also beautifully shown by this one- 

 sixth. 



It seems to me that it is a great 

 mistake to put a wide-angled object- 

 ive — even though it be homogeneous 

 immersion— in a non-adjustable mount, 

 for it so frequently happens that the 

 length of body or density of the im- 

 mersion fluid varies from that for 

 which the objective was originally cor- 

 rected, and in such cases the best per- 

 formance of the objective is lost. Not 

 only should it be adjustable, but it 

 should have sufficient range of ad- 

 justment to correct for water, as water 

 is far better suited to work over tem- 

 porary slides than either glycerine or 

 homogeneous fluid. 



Pond Life in Winter. 



Mr. E. Wade Wilton, in a short arti- 

 cle vcv^ho. Journal oi the Postal Micro- 

 scopical Society, gives some useful 

 information about the microscoi^ic life 

 to be found in ponds in winter. Con- 

 trary to the prevalent idea, a great 

 number of beautiful and interesting 

 forms of life can be found in the mid- 

 dle of winter, under ice a foot thick or 

 more. One of our richest collections 

 of Volvox was made in a pond covered 

 with ice, through which we had cut a 

 hole with an axe, large enough to ad- 

 mit a small collecting net, or bottle. 

 The water teemed with Volvox, and 

 near the bottom Cyclops and Daphnia 

 were found in great abundance. 



Infusoria are to be found in great 

 numbers under the same conditions. 

 Mr. Wade-Wilton, in the article refer- 

 red to, states the conditions under 

 which the infusoria develop in greatest 

 abundance, as follows : — 



" Those microscopists who keep an 

 aquarium, and are in the habit of 



