Miscellanies. 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- 

 rate particles will arrange themselves by mutual attraction, much more 

 regularly than the grinding and polishing can possibly leave them ? 

 and may we not in this way hope to lessen the dispersion, or at least 

 its irregularity ? 



It is said that the alkalies render glass liable to a slovi^ 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. 1 have no chemi- 

 cal apparatus, and my circumstances will not permit me to make the 

 necessary 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. 



11. Parasite of the eggs of the Geometra vernaia. — In Volume 

 xxxviii, (p. 385) of this Journal, was given some account of a spe- 

 cies of Piatygaster which attacks the eggs of the moth {Geometra 

 vernata, Peck,) whose larves have so often devastated our apple trees 

 and elms. At the time that account was communicated, I knew no- 

 thing of the metamorphoses of the insect. On the ISih of June last, 

 after this year's brood of canker-worms (as tliey 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 

 eggs, which I laid 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. 



