264 
NOTES AND MEMORANDA. 
Notice shall always be sent by members to the secretary, one week 
previously, if practicable, of any change of post-office address, or of 
any absence from home which would cause more than ten days’ delay 
in the forwarding of any package directed to them. 
14. The secretary shall annually submit a detailed statement of 
receipts and expenditures to the managers, who shall audit the same 
on behalf of the club . — American Naturalist , April, 1875. 
A Micro-polariscope and Lantern. — We learn from the ‘ Proceed- 
ings of the Academy of Natural Sciences ’ of Philadelphia, that at its 
meeting on the evening of February 2, 1875, Professor Persifor 
Frazer, jun., exhibited a combination of the polarizer, vertical lantern, 
and microscope, by means of which the manner in which different 
salts crystallized out of their solutions, together with the manner in 
which they affect polarized light, was explained and illustrated by 
solutions of potassium chlorate and urea in alcohol. The light from 
a lime lantern is passed through the elbow-tube polarizer, thence 
upward through the vertical lantern and the 2-inch lens microscope, 
when it is again reflected horizontally on the screen. After the 
formation of the crystals had been shown by plain polarized light, 
the analyzer was inserted and the characteristic colours of polariza- 
tion produced. It was explained that while this method had the 
advantage of so magnifying the crystals produced from small quan- 
tities of solutions that their structure could be minutely observed, as 
well as the sudden molecular change which caused the polarizing 
effect, it was open to the objection of a very large loss of light — first, 
by the polarizer, and again by the microscope. It was suggested that 
a means of obviating at least a part of this difficulty would be the use 
of the parabolic reflector, in connection with the first condenser. 
Professor Frazer then proceeded to exhibit the microscopic structure 
of thin sections of some of the Palaeozoic rocks found in York and 
Adams Counties, Pa. A map of the region whence the specimens were 
collected was first thrown on the screen and the geological formations 
described. After explaining the manner in which the thin sections 
were prepared, the following specimens were exhibited : A piece of 
diorite from the north-eastern corner of Saxony ; a foliated chlorite 
slate ; ferruginous gneiss ; Nes’silicon steel ore ; diorite ; quartzite 
rock, with magnetic iron ore, from the north-eastern part of York 
County ; hornblende slate ; limestone, containing particles of a sub- 
stance probably apatite ; a syenite from Germany, with hornblende, 
quartz, and orthoclase ; and a syenite from near Gettysburg. 
