390 Miscellanies. 



any system in the distribution of water, and London, Glasgow, Edin- 

 burgh and Philadelphia are now more advanced in this respect, than 

 Paris. This city however will soon have no cause to envy others on 

 this head. Eighty thousand cubic metres, brought by the canal de 

 I'Ourcq, are to be daily devoted to the embellishment of the places and 

 promenades of Paris, to the watering of its streets and the washing of 

 its sewers : and forty thousand metres drawn daily from the Seine by 

 steam engines, are to be conducted through iron pipes to receivers in 

 every house at different heights according to the wishes o{ the owners. 

 Rev. Encyc. April, 1830. 



2. Optical Instruments. — In a Report of Francoeur, relative to the 

 optical Instruments of Lerebours, Cauchoix, et Vincent Chevallierj 

 it is stated that M. Cauchoix being in possession of a piece of Gui- 

 nand's flint glass, has worked it into an objective of eleven inches di- 

 ameter and eighteen feet focus ; that this beautiful piece constitutes part 

 of the telescope which Mr. South has used with so much effect in Eng- 

 land. A recent letter from this distinguished astronomer to the Re- 

 porter, informs him that he can easily perceive with this instrument 

 nebulous stars whose existence was contested, and that he had dis- 

 covered others, impossible to be observed with any other instrument. 

 Rock crystal is less dispersive, and more refractive than any crown 

 glass, and the employment of it would be exceedingly valuable in 

 large telescopes, but the working of this substance is extremely diffi- 

 cult on account of its hardness and its double refraction. The sub- 

 stitution of this crystal for crown glass, shortens the length of instru- 

 ments one third. The two rings of Saturn may be seen distinctly with 

 a telescope of this kind, of only thirty inches focus and forty five 

 lines of aperture. This result is due to M. Cauchoix. This able 

 mechanist has also resolved the important problem of constructing the 



supports of a telescope so as to sustain the centre of gravity at every 

 inclination, without which it is difficult to use long instruments, for 

 the more a telescope magnifies, the more rapid is the motion of stars 

 in the field of view, and the more difficult it becomes to keep the axis 

 properly directed. He has therefore rendered an eminent service to 

 Science by his ingenious movable support. The gold medal was 

 adjudged to him for his improvements. 



The silver medal was granted to V. Chevallier, pere et fils, for their 

 improvement in microscopes. They have made achromatic lenses of 

 four, three, and even two lines focus. They were the first to con- 

 struct the Amician microscopes and this philosopher has acknowl- 

 edged that their instruments magnify to the extent of six or seven 

 thousand times.— Bull. D'Encour. May, 1830. 



