ASTRONOMY AND METEOROLOGY. 385 



sky, caused by the multitudinous reflections of the sun's light in, the 

 atmosphere outside of the observatory, and therefore altogether irreme- 

 diable by any contrivances within. It is an evil only to be met by 

 establishing the telescope on the top of a very lofty mountain, as on 

 some of the inhabited parts of the Himalaya range, 16,000 and 18,000 

 feet above the level of the sea, where there would be but half the quan- 

 tity of atmosphere to battle against, and that of a much purer and more 

 transparent quality, and free from a cause which was very disturbing, 

 on some occasions, even within the observatory, atmospheric dust. 



PROFESSOR MITCHEL'S SYSTEM OF ASTRONOMICAL OBSERVATIONS. 



AT the meeting of the American Association, in 1850, at New Ha- 

 ven, Prof. Mitchel, of Cincinnati, announced some important improve- 

 ments effected by him iu the observing of right ascensions and declina- 

 tions. In regard to these improvements along and spirited discussion 

 took place, the practicability of the plan being doubted by some mem- 

 bers. To settle the question, a committee of investigation was appointed, 

 with instructions to examine the apparatus of Prof. Mitchel, and report 

 at a future meeting of the Association. The committee consisted of 

 Profs. Peirce, Coffin and St. John, Sears C. Walker, and Capt. Wilkes. 

 At the meeting of the Association, in Cincinnati, May, 1851, the fol- 

 lowing report was submitted and accepted : 



1. Professor Mitchel's apparatus for observing right ascensions is 

 thought by the committee to sustain all his claims in regard to its sim- 

 plicity, accuracy, facility and despatch. It is a fine specimen of ingen- 

 ious contrivance, and the best proof of its superiority in this respect 

 is the fact that, notwithstanding the roughness of construction to which 

 the inventor has been forced to submit by his limited resources, it rivals 

 in the accuracy of its results the most finished specimens of skilful 

 workmanship. By the use of two pens he has avoided all possibility 

 of the peculiar error which must constantly arise whenever the same 

 pen is used for recording the observations and the clock-beats. By re- 

 cording upon a disc with a pencil, which makes a slight dot at a single 

 swift stroke, he has reduced to a minute quantity the perturbations in 

 the motion of the disc which arise from the act of recording. The 

 methods for adjusting the disc and reading its record exclude all dan- 

 ger of error from imperfect centring, while the ingenious apparatus for 

 reading admits of great nicety and rapidity in the execution of this 

 task. The attention which has been paid to the determination and 

 elimination of minute sources of error, such as armature, time, and the 

 like, deserves high commendation. 



2. In regard to the apparatus for observing declinations, the com- 

 mittee report, in some respects, with less confidence, because the series 

 of observations, although quite various, is not yet sufficiently extensive. 

 They think, however, that they may venture to report upon the proba- 

 ble capabilities of the apparatus, and the limit of accuracy which it 

 may be expected to attain, and which it may already have attained. 

 The principles of its construction are regarded by the committee as per- 

 fectly correct, and as exhibiting a happy combination of ingenuity and 



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