there is a thin and observable tuft of whitish hair: the nose and muzzle are black. The tail is bushy like that of the fox, and is divided in the middle by a ring of black, above which, or towards the insertion, the colour is nearly the same as the general tint of the body; but below, or towards the tail, it is white.

The dog, the wolf, and the byæna, correspond in having six grinders in the upper jaw, and in the lower seven. They also agree in the form and number of their

ribs, and lumbar vertebræ, having seven of the latter. Their ribs, of which there are thirteen, are thin and narrow. But both in the striped and spotted hyæna they are fifteen in number, and of an extraordinary breadth; and are proportionally much stronger and larger than in any quadruped of their size: in these, the grinders are only four, or at most five, and the lumbar vertebræ not more than five.

The present animal, therefore, with respect to its teeth, ribs, and lumbar vertebræ, would be arranged in the genus Canis, from which it differs, however, in having only four toes on each foot, and it is said in other essential particulars. With the genus Hyæna it agrees in number of toes, but differs from it in bulk, and in the conformation of the skeleton. These differences were first noticed by Mr. Brookes, who considers it as forming a new genus.

Mr. Burchell, from whose Travels in Africa, vol. ii. p. 229, the above account is taken, informs us that he had one of these animals in his possession for thirteen months chained in a stable-yard, and that, during that time, its ferocious nature deterred every person from attempting to tame it; but it became at length so much softened in manners as to play with a common domestic dog. The man, however, who fed it, never durst venture his hand upon it.

Annual return of Migrating Birds to the same spot.

The late Dr. Jenner, in a curious paper on the migration of birds, published since his death in the Philosophical Transactions for 1824, mentions the following curious experiment: "At a farm-house in this neighbourhood, I procured several swifts, and by taking off two claws from the foot of twelve, I fixed upon them an indelible mark. The year following, their nesting places were examined in an evening, when they had retired to roost, and there I found several of the marked birds. The second and third similar search was made, year a and did not fail to produce some of those that were marked. I now ceased to make an annual search; but, at the expiration of seven years, a cat was seen to bring a bird into the farmer's kitchen, and this also proved to be one of those marked for the experiment.

ARGAND LAMPS, having hollow cylindrical wicks placed before reflecting mirrors, are now generally used for light-houses. A number of lamps are fixed together on a frame, and protected from the weather by glass windows. They are

generally fed with oil, but in a very few places with pit coal gas.

In many of the light-houses on the British coast, the frame in which the lamps are fixed is made to revolve by means of clock-work, so that to a spectator, situated in the

circle of which the light-house is the centre, the light appears at its brightest at the end of a stated period of time, which is generally one or two minutes. The revolving of the light enables the seamen to distinguish the light-house from the light of lime-kilns or other fires upon the coast. This distinction is of great importance, for shipwrecks have often happened in consequence of their taking the light of lime-kilns for the light of the light-house not far distant. The light is, in some light-houses, made

of a red tinge to distinguish it from some other light-house not far distant. The red colour of the light is produced by placing windows of red glass before the lamps. Red is the only colour that can be given to the light in this way. When stained glass of other colours is, placed before the lamp, it is not found to produce a change in the colour of light seen at any distance; the blue or green colour of the glass becomes insensible when seen through a great body of air, which has itself a blue colour.

To the Editors of the GLASGOW MECHANICS' MAGAZINE. GENTLEMEN, Amongst practical men of my acquaintance, I have often witnessed warm debates relative to the quantity of water necessary to condense a given quantity of steam; or, in other words, the quantity of injection water necessary for a steam engine of given dimensions. The insertion of the following explanation and formula, for their information, will much oblige,

GENTLEMEN, yours, &c.
B. R. D. R.

Glasgow, 15th Feb. 1825.

The safety valves of almost all boilers, in this part of the country, are loaded with 3 lbs. or 34 lbs. for each square inch of their area. Taking 3 lbs. in the present enquiry, the temperature of steam necessary to balance this pressure, according to the best experiments, is that of 2230 of Fahrenheit; but, besides this, there is 9400 not indicated by the thermometer, which makes the real temperature equal to 11630 now, 1 cubic foot of steam, at this temperature, when condensed, measures 1 cubic foot of water-calling the temperature of the cold water 500 and that of the warm water 100o. We must

deduct 1000, the heat of the water formed by condensation, from 1163, which leaves 1063 to be communicated to the injection water; and, since each cubic inch of this water requires 500 of heat to make it of the same temperature with the hot; 1063 well, or 21.06, exhibits the 50 number of cubic inches of water necessary to condense one cubic foot of steam. From this is derived the following formula:

Leth the sensible and latent heat of the steam; a the temperature of the cold water; b = the temperature of the warm water; the cubic inches of water

necessary to condense; q, the quantity of steam to be condensed. Then q x h − b = xxb-a: thereh b

fore, xqx