326 Royal Astronomical Society. 



new circles, was ready to be commenced, and he was thereby thrown 

 entirely upon his own resources. 



Colonel Everest resolved to construct the new tables and azimuth 

 circles of cast-iron, which, though objectionable on account of its 

 liability to rust, has the advantage of being lighter and less yielding 

 than brass. The circles were inlaid with gold to receive the gra- 

 duations ; and at every tenth degree a circular disc of silver was let 

 in, so that the large figures might stand prominent. Each was sup- 

 plied with a strong edge-bar below, which put all yielding out of 

 the question, and moreover was of great service in the process of 

 graduation, by affording a support on which to affix the reading 

 microscopes. With respect to the mode of dividing the circles, 

 Col. Everest states that, being aware of the dilatoriness and diffi- 

 culty of any method he had seen detailed, he devised a plan of his 

 own, whereby the divisions of the original circles should be copied 

 on the new. "Without the aid of drawings, it is scarcely possible 

 to impart an idea of the mechanical means which were employed 

 for carrying this plan into effect. The two circles, the new one 

 which was to be graduated, and the old one from which the graduation 

 was to be copied, were placed the one directly over the other, and 

 strongly secured by screws ; and the principle of the method con- 

 sists in keeping the circle to be graduated, which is placed below, 

 steadily fixed on a substantial pillar of masonry, and making the 

 circle to be copied from revolve above it, carrying with it the 

 cutting-tool and clamp : and the apparatus being thus arranged, it 

 is obviously only necessary to apply sufficient means of reading off 

 the angular spaces passed over by the latter in its rotation, in order 

 to transfer its graduation to the former. The mode of operation was 

 assimilated to that which is followed in taking angles. A skilful 

 person was appointed to each of the four microscopes ; the different 

 readings were made precisely equal to the arcs to be intercepted ; 

 and when the one mean reading subtracted from the other showed 

 this value, the order was given to cut. 



The author describes in minute detail the different parts of the 

 operation, which appears to have been executed successfully, and 

 he concludes his paper with an investigation of the mathematical 

 relations of the method, and particularly the effect of eccentricity 

 of the upper circle, and of any error in fixing the cutting-tool, 

 whereby its point would be made to move obliquely to the radius. 



Transits observed at Washington (United States), from January 

 1 to July 1 , 1 840 ; and Occultations observed at the same place, 

 since June 1839. By J. Melville Gillies, Esq. 



The transit is one of the 6-feet instruments made by Troughton 

 for Mr. Hassler, in 1815, and mounted on substantial granite pil- 

 lars. The usual methods were adopted for determining its errors 

 of level and collimation, and the observations are free from all 

 such. The deviation in azimuth was determined from the observed 

 and true differences of right ascension of high and low stars, and 

 registered in its proper column ; but the proportional part due to 

 each observation was not in any case applied. The observations 



