TRANSACTIONS OF SCIENTIFIC SECTION. 17 
interesting species of Primitia, Beyrichia, Isochilina and 
Leperditia. 
There are also a large and fine Plumulites, a new spe- 
cies ; a new species of Metoptoma; a large and peculiar 
Pterotheca, a Murchisonia, perhaps new, and several in- 
teresting new forms of small trilobites. Among these are 
two species of Encrinurus, related to Encrinurus Mirus. 
I have collected a large amount of this material for fu- 
ture study, as this very remarkable ledge is being gradu- 
ally cut away and carried off in the improvements on the 
railway. Before long, the most fossiliferous portions 
will be probably entirely removed and covered up in the 
railway embankments. 
MARCH 27, 1888—SIXTY-SECOND REGULAR MEETING. 
Charles N. Arnold, chairman, presiding. 
The ‘‘ blizzard’ of March 12-15 summarily postponed 
the address which was to have been given March 13. 
Ten members and about fifty guests being present, 
Charles L. Bristol presented ‘‘Some Notes on Amateur 
Photography.”’ 
The paper was discussed by Professor Cooley, Mr. Els- 
worth and others, and an interesting exhibition of flash- 
light photography was given, followed by the develop- 
ment of the negative in the presence of the audience. 
APRIL 10, 1888—SIXTY-THIRD REGULAR MEETING. 
Charles N. Arnold, chairman, presiding ; six members 
and several guests present. 
The following paper was read by Professor Le Roy, C. 
Cooley, Ph. D.: 
LIMIT OF VISIBILITY FOR MINUTE MASSES. 
BY LE ROY OC. COOLEY, Ph.D. 
By solution, asolid is broken into very minute parti- 
cles which are uniformly distributed through the sol- 
27 
