117 



May 17th, lOh. 25m. The comet, though at a very low 

 altitude and with strong moonlight, was still very easily seen 

 with the 5-inch achromatic, and did not appear to have 

 diminished since the 14th instant. This was the last oppor- 

 tunity I had of observing it. 



Lalandes stars Nos. 19168 and 17987 occur in Bessel's 

 Zones Nos. 454 and 347, and Bessel's places have been used 

 in making the reductions. 



Mr. Baxendell, referring to the photographed mircometer 

 which he had alluded to in his paper, remarked that, at the 

 late Meeting of the British Association, Sir David Brewster 

 read a paper suggesting the application of photography to the 

 construction of micrometers for astronomical purposes, but he 

 did not appear to be aware that a micrometer prepared in that 

 way had actually been constructed and in use for some years. 

 The idea of employing photography for this purpose had 

 apparently occurred to diflferent persons, independently of each 

 other, but the credit of having been the first to reduce this 

 idea to practice belonged, Mr. Baxendell believed, to Mr. 

 Dancer, who, in the early part of the year 1858, furnished 

 him with a micrometer consisting of a system of cross lines, 

 neatly photographed on a small glass plate, which by a proper 

 adapter could readily be placed in the field of view, in a plane 

 perpendicular to the axis of the telescope and with the 

 collodion side of the plate next to the object end of the 

 instrument. He had since had this micrometer in constant 

 use for differential observations, and the results he had 

 obtained were quite as satisfactory as any that could be 

 obtained by the more elaborate and expensive reticle micro- 

 meters in ordinary use. 



Some remarks having been made by Mr. Atkinson and 

 Mr. Vernon respecting the vibrations of the barometric 

 column which frequently take place during gales of wind 



