Genus Tachyphonus. 69 



of ornithology, some years ago, by public sale, put me in pos- 

 session of this, and several other little-known birds, from the in* 

 terior of Buenos Ayres. 



Bill T 6 ff , wings, 2£, tail 2£, tarsi -&. 



There is an evident affinity between this and the two preceding 

 species in their general habit, and in the disposition of their 

 colours ; but the bill, which in T. cristatus is thick and compara- 

 tively short, becomes more slender and attenuated in T. Desmaresti, 

 and we are thus prepared for the still greater weakness of this 

 organ in T. tenuirostris ; nevertheless, in all these species, the ty- 

 pical characters are more or less preserved. It may be added that 

 these characters of the bill can even be traced in the Tanagra 

 velia, and this bird may probably connect Tachyphonus with the 

 genuine Tanagers. 



There are several other South-American birds, arranged in the 

 old genus Tanagra, which seem to bear an affinity to this group ; 

 but as they are only known to me by the descriptions of Dr. 

 Latham, or the figures of Buffon, I cannot venture to give them a 

 place in the present monograph. 



Art. XL Supplement to a Paper on the Vibrations of 

 Heavy Bodies, in the Fifteenth Volume of this Journal. 

 By Davies Gilbert, Esq. M.P., Treas. R.S., &c. 



Having inserted in the XVth volume of the Quarterly Journal, a 

 Paper on the vibration of Heavy Bodies in cycloidal and in circular 

 arcs, I am now desirous of adding a supplement to the part, which 

 relates to the variation of time, occasioned by different buoyancies 

 of the atmosphere, as the barometer rises or falls. 



My attention was first directed to the subject by the late Doctor 

 Maskelyne ; and as it appears from a very simple calculation, that 

 each inch of variation in the height of the barometer must change 

 the daily rate of a clock connected with a brass pendulum, about 

 two-tenths of a second, in so far as buoyancy is alone concerned ; 

 I constructed a table for each hour, and for every tenth of an inch. 



Having requested Mr. Pond and Doctor Brinkley to observe the 

 rates of their clocks, when the barometer stood at its opposite ex- 



