MICROSCOPY. 565 
ture found to pertain to some of my immersion objectives in balsam, in water and in 
air. 
Air, Air, Water. Balsam, 
Single Front. 1-18 in. 170° 120° 87° 
T “ 1-18 in. 170° 110° 88° 
Compound Front. 1-10 in. 175° ur 95° 
iy ST 1-13 in. 175° 105° 
r z 1-6 (high) 172° 106° 88° 
Single r 1-5 in. 175° 127° 110° 
evarying diff between the water and balsam angles can, in a general way, be 
nted for from the formulas of construction differing iderably, each one from 
any other. ; 
ce 
1l tl bjectives tł t effective (especially when its low power is considered) 
is the 1-5 in. of 110° in balsam. This is true of its use for objects mounted in balsam, as 
Rhomboides, small. But notably so as to its work on dry A. pellucida. My London 
Specimen of this, received through the U. S. A. M ve 
Shine, I may say. The illumination I used was petroleum lamp flame, no conden- 
Bal With the same means al? the objectives show A. pellucida with the same illu- 
mination, but with a difference. 
With sunlight and a blue cell no doubt the higher powers would have their proper 
advantage, : 
Itis proper to mention that the 1-5 in. of 110° balsam angle was constructed on the 
plan proposed by me in the Lon. “ Month. Micr. Jour.” for March 1872, where I have 
made use of a diagram by Mr. Wenham of a 1-8 in. of his construction, to indicate 
modifications such as would give more than 81 ° or 82° in balsam. 
With proper appliances below the balsam-slide (as pointed out by me in the Lon 
bl 
large angle must have access to and throngh the balsamed object from below; in the 
next place the objective must be capable of receiving and transmitting that dimension 
of pencil to the which thing previous to my own demonstrations has not been 
own to have been done. 
With much respect, yours truly, 
Bostoy, July 8, 1872. ROBERT B. TOLLES. 
OrGantsms in Croron Warer.— Chas. F. Gissler’s pamphlet 
on this subject can be obtained of the Naturalists’ Agency, though 
not so stated on the title page. While microscopists gener- 
ally are now approaching this question of water supply from a 
utilitarian direction, seeking hints of healthfulness or pestilence 
ate the organisms they detect, the author looks upon the Croton 
with inquisitive eyes, deeming the water New Yorkers drink a 
charming field for chasing rotifers and crustaceans, water-bears 
and worms, and scarcely giving a thought to their dietetic value. 
As far as can be gathered, he judges them healthy enough, with 
araea comparatively unimportant exceptions. The pamphlet con- 
tains some very attractive plates, which are well calculated to 
accomplish the author’s avowed object, giving encouragement and 
Popularity to this branch of microscopical study. 
z Distripvrron AND Action or Nerves.— Dr. L. S. Beale and 
Dr. E. Klein have contributed valuable papers on this subject to 
