1'HILOSOPHICAL TKANSACTIONS. [aNNO \77Q. 



serves to set it in such a position, that the centres of the 2 lenses may be in the 

 plane of a vertical arch. This level is also used for adjusting a small quadrant, 

 which is fixed to it, and divided into degrees, to show the elevation of the tele- 

 scope when directed to the star ; then the quantity of refraction answering to 

 that altitude may be found by the common tables, and the concave lens set ac- 

 cordingly, by means of the scale at the side, whicli is divided into half minutes, 

 and, if required, by using a nonius, may be divided into seconds. 



It must be observed, that when a star or planet is but a few degrees above the 

 horizon, the refraction of the atmosphere occasions it to be considerably 

 coloured. The refraction of the lens acting in a contrary direction would exactly 

 correct that colour, if the dissipation of the rays of light were the same in glass 

 as in air ; but as it is greater in glass than in air, the colours occasioned by the 

 refraction of the atmosphere will be rather more than corrected by those occa- 

 sioned by the refraction of the lens. 



A drawing of the refraction apparatus is added, which may serve to give a 

 more clear idea of it. See pi. 5, fig. 7. 



A A, the circular brass tube, which fits on to the end of the telescope, bb, tlie oblong concave 

 lens in its frame, which slides over the fixed convex lens, c, the circular spirit level, which shows 

 when tlie oblong lens is in a vertical arch, d, the quadrant to which the spirit level is fixed, for 

 showing the angular elevation of the telescope, e, the milled head fixed to a pinion, by which the 

 whole apparatus is turned round on the end of the telescope, in order to set the oblong lens in a ver- 

 tical arch. F, another pinion for setting the quadrant to the angular elevation of tlie telescope. By 

 means of these 2 pinions the air bubble must be brought to the middle of the level, aa, is tlie scale, 

 with divisions answering to minutes and half minutes of tlie refraction occasioned by the concave lens. 



XXlf^. Experiinenln and Observations on Iriflammable Air breathed by 

 various Animals. By the Abbi Fontana,* Director of the Cabinet of Natural 

 History belonging to his Royal Highness the Grand Duke of Tuscany, p. 337 

 Philosophers believed, till lately, that inflammable air had the power of kil- 



* The Abbe Felix Fontana died at Florence in 1805, at the age of 76. He was director of tlie 

 Florentine Cabinet of Natural History, and member of several learned societies. His scientific pur- 

 suits were so numerous and varied, that, while in healtli, he scarcely allowed himself a moment's 

 leisure. Hence he was enabled to conduct that astonishing number of experiments which we find 

 recorded in his philosophical works, and to execute the most curious models in wax, (some of which 

 and especially the anatomical models, must have required a large portion of time and extreme nicety 

 of labour) besides his 2 wooden statues, which may be taken to pieces, so as to exhibit, \\\i\\ the 

 utmost exactness, the structure of every part of tlie human body. These statues, one of which lie 

 left unfinished, are composed of several thousand different pieces. 



Besides the papers inserted in the Phil. Trans, and in Rozier's journal, and some separate tracts on 

 eudiometry, and on nitrous and dephlogisticated air, the Abbe Fontajia wrote 0.sservazioni sopra la 

 Ruggine del Grano, 17()7 ; Osservazioni sopra il filso Ergot e la Tremella, 1775 ; and Traite sur le 

 Venin de la Vipere, 2 vols. 4 to 1781. It was this last work which procured its author tlie distin- 

 wjuislied rank which he held among modern physiologists and experimenters. In this work fpart of 



