344 History of Mechanical Inventionsy and 



complete robe with the sleeves, but without seanns. In order to give the tis- 

 sue a regular form, the caterpillars are limited in their motions, and inter- 

 dicted from particular parts by oil, which they dislike, and upon which 

 they will never work. Hence he made them fabricate a stuff which ap- 

 peared as if regularly stitched. One or two insects can weave a square inch 

 of cloth. 



. This cloth exceeds in fineness the lightest gauze, and a specimen of it 

 sent by M. Paret of Stockholm was exhibited by M. Lcnormand to the 

 Academy of Sciences of Paris. 



- The air balloon above-mentioned weighed only five grains, and yet it was 

 impervious to air. The heat of the hand instantly inflated it ; and the 

 flame of a single match held for some seconds beneath it caused it to rise 

 to a considerable height in the air, where it remained for half an hour. 



A shawl an ell square was, when extended, blown into the air by a 

 shght puff, when it was like a light vapour gently agitated by the wind. 



M. Habenstreet offered a shawl to M. Paret, on condition that the 

 latter would cause it to fall from the air upon his head, but this was im-. 

 possible, for, as the shawl approached his body, the heat which rose from it 

 repelled the shawl into the air. 



A complete robe of this stuff was worn by the Queen of Bavaria over 

 her dress on court days. 



The fibres of this fabric, of which the caterpillars form their coccoons, are 

 not interlaced, but merely superposed, and this act takes place the moment 

 the insect secretes the matter of the fibre. M. H. gives it increased soli- 

 dity by compelling the insects to labour several times over the same sur- 

 face. A shawl an ell square costs at Munich only eight francs. 



M. Lenormand, from whose memoir the preceding facts are taken, sug- 

 gests, that, as the caterpillar which forms thefusain (^EuonymusEuropasusJ 

 and which is common in France, spins its threads and forms its tent in a 

 similar manner, its labour might be employed for the same purpose.— 

 Abridged from Newton's Journal of the Arts, December 1827, p. 214. 



3. Radii of the surfaces of a Double Achromatic Object-Glass, By M. 



Lit TROW. 

 The index of refraction of the crown glass being 1.53, and that of the 

 flint glass 1.60; their dispersive ratio 0.25, the thickness of the crown 

 lens 0.01, and that of the flint 0, and the lenses being supposed in contact, 

 the best radii will be 



Crown lens equally convex, radius of each surface, 10.6 



Flint glass lens double concave, radius of 1st surface, 1.04-394 



2d surface, 3.296512 

 • Focal length, . . - . 3.70'2231 



Aperture, - - = Focal length, X 0.09973 



That is, the aperture will be 1-lOth of the focal length, which is a much 

 larger proportional aperture than it is usual to give to achromatic telescopes. 



4. Exhibition of the National Industry of France 

 This great exhibition of the production of the arts, sci 



arts, sciences, and manu* 



