—— 211 
6. If we can render glass very fluid in the melted state, and cast 
lenses in finely polished moulds, is it not highly probable that the sepa- 
_ Yate particles will arrange themselves by mutual attraction, much more 
regularly than the grinding and polishing can possibly leave them ? 
and may we notin this way hope to lessen the dispersion, or at least 
its irregularity? — 
It is said that the alkalies render glass liable to a slow decomposi- 
tion. If we could make transparent glass of alumina and bismuth, I 
have reason to believe that we should obtain great refractive power, 
very little dispersion, and great fluidity in the melted state, which are 
important desiderata; but it is highly probable that any combination 
with alumina would produce an opake enamel. I have not heard of 
any experiments made for these specific purposes. I have no chemi- 
cal apparatus, and my circumstances will not permit me to make the 
hecessary experiments; I therefore hope that some of the scientific 
readers of the Journal of Science, who have leisure and fortune, will 
feel so far interested in the subject, as to ascertain the facts in relation 
to these inquiries, as well as such others as experience may suggest, 
and finally inform us all of the results. A. Bourne. 
Chillicothe, Ohio, Dec. 17, 1840. 
ll. Parasite of the eggs of the Geometra vernata.—In Volume 
Xxxvi1, (p. 385) of this Journal, was given some account of a spe- 
cies of Platygaster which attacks the eggs of the moth (Geometra 
vernata, Peck,) whose larves have so often devastated our apple trees 
andelms. At the time that account was communicated, I knew no- 
thing of the metamorphoses of the insect. On the 13th of June last, 
after this year’s brood of canker-worms (as they are popularly called) 
had passed into the earth, I noticed on the fences several clusters of 
eggs still unopened. Knowing that many of these very eggs had, 
during November, 1839, been visited by the parasites above men- 
tioned, I examined them carefully. The one which I first opened, 
contained a single parasite in the perfect state, and ready to come 
forth. The insect was evidently glad to be released, and after going 
through with the usual adjustments, walked away. In each of seve- 
ral other eggs which I opened, I found a single parasite. They were 
in various stages of development, but most of them so far advanced 
as to show the features of the perfect insect. Most of the remaining 
€ggs, which I Jaid aside, were, a few days after, found open. A few 
weeks later, I observed that nearly all the eggs on the fences, most of 
which were whole on the 13th of June, were now perforated at the 
top, doubtless by the parasites eating their way out. 
