The Quarterly Journal

Tanagra cristata. Linn. Syst. Nat. 317. Index Orn.

Tanagra cayennensis nigra cristata. Brisson Ornith. append. p. 65, tab. 4, f. 3. Hauppette. Buffon Pl. Enl. 7, fig. 2.

Desmarest Hist. Nat. des Tanagres, pl. 47. Crested Tanager, Lath. Gen. Synopsis 2, p. 221.

Description.-Bill entirely black, strong, and rather dilated at the base; the rictus furnished with a few weak bristles, and the margin of the upper mandible considerably sinuated. The crown of the head is covered by a conspicuous crest of bright orange-red, having the margins paler and more of a fulvous yellow. The general colour of the plumage, both above and beneath, is brownish black; across the rump is a broad band of fulvous, and beneath the chin is a short stripe of the same colour, extending half way down the throat: part of the scapula, and the whole of the inner wing-covers, are pure white; wings brown; tail black, and rather lengthened; tarsi brown.

This species appears subject to some variation in the colour of the crest, and in the extent of the fulvous stripe on the throat. But as these varieties have not come under my own observation, I must refer the reader to the admirable work of M. Desmarest on this family. The above description has been taken from the male bird as it usually occurs in Brazil: the female I have never seen. I have frequently had occasion to observe, that where the same species is found both in Cayenne and Brazil, the specimen from the former country is invariably larger and more richly coloured may not this be attributed to the excessive heat and humidity of that province, which may be supposed to affect the animal productions no less than those of the vegetable world?

8. TACHYPHONUS Desmaresti. Sp. Nov.

T. violaceo-niger; cristá uropygioque fulvis; crisso rufo; tectricibus inferio ribus niveis.

Glossy black; crest and rump fulvous yellow, vent rufous; under wing-covers snowy. Pl. Enl. 301, f. 2.

Description.-Size of T. cristatus; but the bill is longer, more slender, and more pointed; and the upper mandible, is less curved, The general colour of the plumage, both above and beneath, is deep

black; glossed with blue in every part but the wings and tail. The crown has a concealed crest of buff-coloured feathers, and on the rump is a broad band of the same tint. The vent and under part of the flanks are deep rufous; tail-covers black; under wingcovers snowy white. On closely examining the tarsi of the specimen in my collection, (the only one I have the means of consulting,) I find they do not naturally belong to the bird. This artifice was formerly much resorted to by bird-stuffers, who thought it no sin to give new legs to a bird when its own were unserviceable.

In the sale catalogue of Mr. Hullet's collection, this bird is stated to have been sent from Buenos Ayres.

Bill, wings 3, tail 3.

Naturalists have hitherto considered this as a variety of T. cristatus, but even admitting that the difference in their plumage is not very considerable, the more lengthened, pointed, and attenuated form of the bill, in this bird, at once points it out as a species intermediate between T. cristatus and T. tenuirostris: I therefore feel happy in recording it under the name of Desmaresti, as a just tribute of respect to that celebrated ornithologist, who has illustrated the Tanagra of Linnæus in one of the most splendid publications of the present day.

9. TACHYPHONUS Tenuirostris. Sp. Nov.

T. violaceo-niger; scapularibus albis; caudæ tegminibus inferioribus rufis ; rostro gracili.

Glossy blue-black; scapulars white; under tail-covers rufous; bill slender.

Description. In its general proportions this is rather smaller than the preceding; the bill, in particular, is much more slender, the culmen more arched, and the lateral margins are more than usually inflexed. The general colour of the whole bird is a deep and glossy raven black; but the scapular, and parts of the lesser wing-covers, are pure white, and the under tail-covers deep rufous. The wings and tail agree in their structure with those of the more typical species. The bill and tarsi are black; and the latter appear rather lengthened. The dispersion of Mr. Hullet's cabinet

of ornithology, some years ago, by public sale, put me in possession of this, and several other little-known birds, from the interior of Buenos Ayres.

Bill, wings, 24, tail 24, 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 comparatively 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 typical 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. XI. 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

tremes, they were so good as to do so; and I learnt, with much surprise, that neither at Greenwich nor at Dublin had the expected variation of rate taken place.

It has been demonstrated by Sir Isaac Newton, that small changes in the resistance to oscillatory bodies do not by their direct action cause any variation in the times of vibration, since the ascending and descending semivibrations compensate each other; but increased resistance reduces the arc, where the maintaining power is constant; and, consequently, it reduces also the circular excess, so that an increased resistance thus indirectly accelerates the time of vibration. This circumstance has been noticed by various writers, and had not escaped my attention; but the quantity seemed so very small as to be wholly evanescent, in comparison even with the minute change of time assignable to buoyancy. On submitting it, however, to calculation, the result proved very different.

Let h express in barometrical inches the density of the atmosphere.

Then since the resistance experienced in moving through any space, is proportionate to the space itself, to the velocity, and to the density of the medium and in the cycloid, or in small circular arches, the space and the velocities of semivibrations are proportionate to each other:

If R be put for the resistance,

and z for the arc,

R = hz.

But resistance is evidently equal to the maintaining power, consequently he is constant; and therefore

22h=2hzz, or zh2hz, and z = z X

whence it appears that in different arcs the variation of the lengths, occasioned by a given variation of the barometer, is proportionate to the arcs themselves.

Now the circular excess in any small circular arc is th part of the arc squared. (See page 10 of the paper referred to.) Whence the variation of this excess; or the fluxion of the time (i) corresponding it hh, will be