166 



strongly recommended, and extensively used, on account of the beauty 

 and truth of one of the theoretical principles involved in it, — ^he 

 recommended a bar-micrometer, wherein right ascensions were raea- 

 sui'ed by transits across three parallel bars, marking both the immer- 

 sions and emersions, so as to get rid of error of focus and irradiation 

 of light ; and declinations were measured by a bar at right angles 

 to the former, the objects being bisected alternately with either edge 

 of the bar. Observers already provided with position-micrometers 

 might easily have some of these bars inserted, which in one position 

 might be used for A. R., and in another for Decl. Such a micro- 

 meter has been found to require no illumination on the darkest nights, 

 even in telescopes of small aperture, and to produce results, with 

 the amorphous masses of faint comets, almost equal in accuracy to 

 those obtained from stars observed with fine wires in an illuminated 

 field. 



The paper concluded with a short special description of the Zod. 

 Light-equatorial, which, for economy, lightness, and general effec- 

 tiveness, seemed well fitted for scientific travellers. 



2. On the Vertebral Column, and some Characters that have 

 been overlooked in the Desci'iptions both of the Ana- 

 tomist and Zoologist. By Dr Macdonald. 



After noticing that the vertebral skeleton has usually been com- 

 pared to a column, of which the basis (in man) is formed by the sa- 

 crum and coccyx, the shaft or columnar part being the bodies of 

 the true vertebrfe, as they are usually styled, and "surmounted by 

 the splendid composite capital the cranium, the author proposed re- 

 stricting the observations to the columnar portion, usually divided 

 into 7 cervical, 12 dorsal, and 5 lumbar vertebras. This division 

 was denounced, and beginning at the summit, he shewed that the 

 upper or cervical region consisted only of 6 vertebra;, as the 7th, in 

 its normal position in the mammal class, had a rib partly articulated 

 to its body, and therefore acquired the character of a dorsal vertebra. 



Restricting the cervical to six, the arrangement of the atlas and 

 axis indicates the tendency to a combination into pairs in the course 

 of the vertebral axis. The body of the atlas is almost entirely re- 

 placed by the intrusion of the odontoid process of the axis ; and thus, 



