114< Dr. Hare on the Cotistruction and Applications of the 



of this species was shot near Crosby-upon-Eden, on the 1 1th of 

 April. The lowest part of the white patch on each side of the 

 neck was only clearly defined : above this were a few irregular 

 longitudinal white streaks, more numerous and distinct on the 

 left than on the right side. 



The Brent Goose is one of our rarest visitants here; whilst 

 on the contrary the Bernacle [A. Bernicla) is a regular winter 

 visitant, and occasionally seen in great numbers. 



Black-throated Diver (Colymbus arcticus). — A speckled 

 Diver was killed in the river Eden about the 7th of February, 

 which from its weight and size* was in all probability an im- 

 matui'e bird of this species. I could not ascertain its sex: in 

 the stomach were three small chubs or skellys {Leuciscus ce- 

 phalus) recently swallowed. An old Red-throated Diver [C. 

 septentrionalis) was killed on the same river on the 17th of 

 April, 1823. Both are of rare occurrence here. Dr. Fleming, 

 in his History of British Animals, appears to think that these 

 two species may eventually prove to be the same ; the latter 

 being the female of the former. 



Carlisle, April 27, 1839. 



XIX. On the Construction and Applications of the improved 

 Sliding-Rod Eudiometer and of the Volumescope. By Robert 

 Hare, M.D. of Philadelphia\. 



Description of an improved Mercurial Sliding-Rod Eudiometer. 



T^HE aqueous sliding-rod hydro-oxygen eudiometer, (see 

 ■' Phil. Mag. vol. Ixvii. p. 21.) although perfectly well qua- 

 hfied for experiments in which water is employed, does not 

 answer well when used over mercury. The great weight of 

 this liquid causes the indications to vary during manipulation, 

 in consequence of changes of position too slight to be avoided. 



The instrument represented in fig. 1. is furnished with a 

 water-gauge O M, which, being appealed to, enables us to 

 cause the pressure of any contained gas to be in equilibrio with 

 that of the external air, and consequently to measui'e it with ac- 

 curacy. Excepting the gauge, the mechanism by which the 

 measurement is eifected is the same as that of the sliding-rod 

 eudiometers for water above alluded to. However, in addition 

 to the stuffing-box at A, there is in the mercurial eudiome- 

 ters a collar of cotton wick soaked in oil, and packed by a 

 screw B, which includes the cotton and compresses it about 

 the rod. The object of this addition is to supply oil to the 

 rod where it enters the collar of leather ; otherwise, they would 

 soon become so dry as to allow air or mercury to pass. 



* Weight, 4 pounds 1 ounce ; Length, 28 inches, 

 t Communicated hy the Author. 



Let 



