SCIENTIFIC SUMMARY. 
219 
the breaking weight of the bar at that temperature, while the average of the 
six experiments at zero gives 4 cwts. 20 lbs. as the breaking weight of the 
bar at zero, being an increase of strength from the reduction of temperature 
equal to 3-5 per cent. Sir W. Fairbairn, in a paper read another evening, 
attributes the breaking of the wheel in railway carriages to irregularity of 
the action of the wheel, caused by alteration in position of the tire. 
MICROSCOPY. 
Noberfs 19 th Band and its Observe rs. — The 11 Monthly Microscopical 
Journal ” for March contains an important paper by Mr. Charles Stodder. 
In it he opposes the statements of Col. Woodward, that he had not 
seen the 19th band on the instruments he asserted he had seen it with. 
He seems very fully to demonstrate his position, but probably there will 
be an answer by Col. Woodward in next month’s number. 
Ho iv to Mount Objects is very well treated of, and discussed by Mr. D. E. 
Goddard, in the “ Journal of the Quekett Club” for January. In the 
same number Dr. Bastian’s views are opposed by Mr. Lowne, and an in- 
genious neutral-tint selenite stage is described by Mr. W. Ackland. 
The Largest Angle of an Immersion Lens . — Mr. Wenham, writing in the 
“ Monthly Microscopical Journal” for January, says that the same optical 
law that limits the aperture of any object-glass to near 82° in a balsam- 
mounted object also determines the angle in the lens at which the rays 
diverge after being refracted from the plane surface of the front. This can 
never exceed 82° in a dry objective ; nor can it be greater on the immersion 
system, where an interchange of front adapts it to both conditions, as the 
very correction which necessitates the form of the back lenses and their 
diameters will not transmit a greater pencil ; and therefore, if the front is 
immersed in balsam for the purpose of viewing an object placed therein, 
this angle of 82° or less, as the case may be, instead of converging at 170° 
as from the dry lens, is continued right to the object, supposing the refrac- 
tive index of the front and balsam to be the same, which they are nearly. 
Phycocgan. — Mr. T. Charles White has described to the Royal Micro- 
scopical Society how this substance came to be developed in a bottle of 
fluid collected in the round- water at Kensington Gardens, and left aside. 
The following are the author’s words: — “Not thinking this worth ex- 
hibiting to my friends, I screwed down the top of my York bottle, and 
stood it on the window-ledge inside my room, and it was there forgotten 
for about a fortnight, when, by chance looking up at it, I saw that the 
green flocculent matter had descended to the dead level of some yellowish- 
coloured mud, but for about a quarter of an inch above it was a layer of 
the deepest richest indigo blue I had ever seen. Taking it down carefully, 
so that no disturbance of it should take place, I looked at it by reflected 
light, when it was a rich crimson lake. I then remembered the dichroic 
fluids I had seen here, and made a careful examination.” This examina- 
tion, however, does not throw more light on the subject. 
Browning's Microscope Lamp , which has been made since our last issue, is 
one of the nicest instruments we have seen. Not only is it complete op- 
tically, but it is admirably handy, packing into a small case, just six inches 
