74 Tue Microscope. 
color varying in thickness from a mere pellicle to probably one- 
eighth of an inch. The upper surface of the thick scum looks 
like bright red dust. I have also often observed deposits of the 
astasia on the bottom of the pond where the water was shallow 
and still. They have regularly appeared in great abundance 
each summer since their first appearance, and probably will ap- 
pear again the coming summer or fall. I commenced a study 
of their life history last September, but did not complete it; 
will resume again next fall, if they appear. I have kept them 
in small aquarias for several weeks very successfully. I also 
deposited a large number of them in a tank, in my greenhouse, 
holding about ten barrels of water and where the temperature 
of the air never goes below 60° F., hoping to be able to con- 
tinue my investigations during the winter, but so far they seem 
to keep out of sight, and I find none of them that I can recog- 
nize with certainty, although, within a day or so past, a form 
has appeared very similar in some respects, but having very 
rapid motions and a distinct mouth, and with ends more nearly 
the segment of a circle. 
I had supposed the astasia a common object, but the sug- 
gestion that it is new to this part of the world invests it with 
new interest. 
My greenhouse tank is supplying an immense amount of 
interesting microscopical life, and possibly I shall favor you 
hereafter with some of the results of studies from that quarter. 
NewcastLe, Ind., January 24, 1884. 
~<om 
MICROSCOPY ONE HUNDRED AND FIFTY YEARS AGO. 
E. A. CONGDON, 
Ne understand the progress of the study of microscopy. it is 
interesting to go back to its earlier periods and compare its 
aims and statements as represented by writers of those by-gone 
times with its present position, and its fund of knowledge ac- 
cumulated since that time, when its earnest students gave their 
statements to the scientific world. ‘ Baker on the Microscope,” 
written in 1740, now seems to us quaint, full of peculiar ideas, 
and wanting in the definite knowledge which the investigations 
