Royal Astronomical Society. 481 



results more worthy of confidence than those made with the existing 

 instruments. It being taken into account, also, that, while only one 

 observation can be made in the day on all stars which are not circum- 

 polar, and only two on some of those which never set, with an in- 

 strument fixed in the meridian, the number of observations which 

 may be made with M. Wettinger's instrument is unlimited ; and as 

 these observations might be made at all altitudes from that when 

 the stars passed the meridian to the moment of their rising or setting, 

 many curious inferences might possibly be deduced from it on the 

 subject of refraction, while the observations might be so arranged 

 as to counteract the vitiating effects of refraction, and, by the com- 

 bination, to give correct results. 



" It would seem that this instrument would be very useful in de- 

 termining the place of a comet by direct observation, instead of in- 

 ferring it, as is usual, even with an equatoreal instrument. For this 

 purpose any standard or other star sufficiently brilliant to bear the 

 triple reflection may be used. 



" It will be observed in Signor Carlini's report, that, a doubt 

 having been expressed as to the possibility of applying the principle 

 of this instrument to the sun, M. Wettinger, in order to try the ex- 

 periment, fixed the small reflector or speculum of his model to the 

 great equatoreal at Milan, in. such a way that, while Sirius was ob- 

 served directly by the telescope, the image of the sun, duly darkened 

 and submitted to one reflexion, was observed in the same apparent 

 direction ; and both, as he informs me, with such perfect precision, 

 that the star could be seen on the disc of the sun, or be brought in 

 contact with the limb with the utmost certainty. 



" It will be observed that Signor Carlini and his colleagues, in 

 their report, advert to the multiplicity of parts and variety of move- 

 ments in M. Wettinger's instrument, as contrasted with the fixed 

 nature and simple operations of the large meridian instruments now 

 in use. But still they appear to be disposed to look with a favourable 

 eye to the capabilities of M. Wettinger's invention, and they seem 

 anxious that one of sufficient dimensions should be made ; but for this, 

 in their opinion, there are no means in Italy, and they recommend 

 Munich or Vienna. Why not London ? 



" M. Wettinger is of opinion that prisms of glass might probably 

 be substituted with advantage in place of the reflectors. 



" As I may probably have omitted some material points in this 

 explanation, I have requested M. Wettinger to draw up a descrip- 

 tion of it in Italian, the only language which he speaks ; and I have 

 asked him to employ the same letters of reference which I have used, 

 so that the same sketches may do for both. 



" I ought to add, that M. Wettinger is one of the professors of 

 the university established here, and that he has long been highly 

 esteemed for his knowledge and ability, and he is a person well ac- 

 quainted both with the principles and the practice of astronomy. 



" Should you wish it, or should you think it would prove inter- 

 esting to the Astronomical Society, to see the model which M. Wet- 

 tinger has constructed, I have no doubt he would readily allow it to 



Phil. Mag. S. 3. Vol. 21. No. 140. Dec. 1842. 2 K 



