117 
May 17th, 1 Oh. 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. 
Lalande's 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 different 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 
