222 
and the varnish poured on until the surface 
is covered, then the excess is drained off one 
corner and the glass is placed in a negative 
rack to dry. For a varnish, any good, trans- 
parent varnish may be used. It should be 
diluted to about one tenth the usual thickness. 
For the diluting substance xylene, toluene, 
turpentine, etc., may be used. Varnish di- 
luted with xylene will dry on the glass in 
about half an hour if the room is dry and 
warm. If turpentine is the diluent it is 
better to let the varnish dry over night. 
If the slide is to be used for a single ex- 
hibition it need not be covered and bound, but 
if it is to be permanent it is better to protect 
the surface by covering and binding as with 
photographie lantern slides. 
If the slides are coated with 10 per cent. 
gelatin and dried one can also use the pen and 
brush well, but the varnish has proved a better 
coating. 
These varnished glasses for hand-made lan- 
tern slides have been in use in different de- 
partments of Cornell University for the last 
six years and have proved very satisfactory. 
It may be well to call attention to the fact 
that nearly all forms of celluloid are in- 
flammable, and slides made of it might bring 
disaster. 
Sion H. Gace 
CoRNELL UNIVERSITY, 
July 30, 1918 
THE HOUSE FLY 
To THE Epritor or Scimnce: The accompany- 
ing paper was written by one of my students 
in elementary biology within one month of 
the opening of the course. It happened that 
the house fly was providing the material for 
laboratory work at that time. And it also 
happened that several students were attracted 
by the inconclusive statements in several text- 
boks regarding the function of the so-called 
balancers—which they had already recognized 
as probably representing the second pair of 
wings. Experiments were thereupon encour- 
aged to clear up the situation. At first re- 
sults were conflicting, owing to excusable de- 
fects in operative technic. Mr. Whealdon, 
SCIENCE 
[N. 8. Vou, XLVIII. No. 1235 
however, succeeded in reaching unequivocal 
results, which he embodied in the report that 
is printed below just as he wrote it. 
My purpose in bringing this report to your 
attention is primarily pedagogical. The facts 
established by Mr. Wealdon can not lay claim 
to novelty, as he later discovered. But the 
method of permitting a student in an ele- 
mentary course at the very beginning of his 
work to occupy himself in laboratory hours 
with a problem he himself had raised and 
frankly to regard such work as a tesearch— 
which indeed it is in every essential—to be 
earried to a real conclusion, quite regardless 
of the activities of the other students in the 
laboratory; this method, which subordinates 
prearranged plans by the instructor to the en- 
couragement of student initiative, may be still 
sufficiently uncommon in American schools 
and colleges to justify submitting the accom- 
panying evidence of its efficiency. 
Harry Beat Torrey 
THE BALANCERS OF THE HOUSE FLY 
Report of Some Hxperiments to Determine 
their Use 
Experiment 1.—I put two flies of apparently 
equal vigor, but differing slightly in size and 
coloring of the abdomen, under the influence 
of ether. From one of them I removed the 
‘balancers by means of very sharp pointed 
scissors. The other I left untouched, using 
him merely as a check, by which I could com- 
pare the actions of the two as they came out 
from the influence of the anesthetic. This 
process I repeated with two more flies, then 
placed them in pairs, one clipped fly with one 
unclipped, under bell jars, and observed their 
behavior. 
Through the difference in size and marking 
I was able to identify the unclipped flies and 
noted that they appear to recover from the in- 
fluence of the anesthetic sooner than the 
clipped flies in both cases. As soon as the 
flies with the balancers removed recovered from 
the effects of the ether they commenced to rub 
themselves with their hind legs, stroking their 
abdomen and wings almost continuously, even 
lifting their legs quite above the wings and 
