Imatges de pÓgina
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L. L.-An index divided, but corresponding with K. to which

the small hands point. This index, as will be seen by

the sketch N, is not essential. M. M.—The case which covers and supports the thermometer. N. A different arrangement of the hands, by which one in

dex is sufficient. For a description of which, refer to

B., C.C., D., E., F., and G. G., as before represented. The modus operandi is so simple as hardly to require a description; for if by the increase or diminution of temperature the mercury in the tube rises and falls, it is evident that the needle will always (from the influence of the magnetic fluid or principle,) point to the centre of attraction within the iron ball floating on its surface; and as the main hand is attached to the needle, it will indicate such changes at the index. The two small hands being brought in contact with the circular rod connected to the main hand, will always be farther separated from each other, as that may rise or fall, and allowance being made for the resistance, show the extremes of those changes. The index should correspond with the movements of the needle and main hand by themselves; then the resistance of the small hands may be readily calculated by any other thermometer with a similar index. As the small hands do not recede, they must, to give a diary of the changes, be daily adjusted.

For the small hands, rings or springs constructed to slide on a wire, &c. may be substituted for registers, but that which moves with the least resistance, should be preferred. If a common sized Florence flask be used for a bulb, and alcohol for the expanding medium, the caliber of the tube should be about four and a half or five lines in diameter, varying according to the size of the flask; when a fluid more expansible than alcohol is used, the diameter should be increased; the most expansible is preferable, as it enables the use of a greater attracting power. This kind of thermometer is not very sensible, but is much more so, than at first would be supposed.

When atmospheric air, or any other compressible fluid, is used for the expanding medium, the tube should be hermetically sealed; under other circumstances, a cork will be found sufficient to protect the mercury from dust and the action of oxygen.

Care must be taken that it always be kept in a perpendicular direction; for if any portion of the expanding fluid be suffered to escape, it will be necessary to add more mercury, or re-adjust the index. It may be plainly or ornamentally cased; and will, I have no doubt, if care be taken in the construction, answer the designed purpose.

We are indebted to a respectable philosophical friend for the following remarks.

Mr. Clark's thermometer for registering the two extremes of temperature within any given period, may serve very well as another variety in addition to those already made for the same purpose. It may, however, be remarked: 1. The magnetic needle, which is used as an index, will be, in

some measure, affected by the general attraction of magnetism, as well as by that of the iron ball, which will affect

its accuracy. 2. Unless the iron ball be of considerable magnitude, its action

on the index will be very feeble, provided this be not very light, in which case its mechanical action on the moveable hands G. G. will be scarcely sensible.



Small-Pox and Vaccination. The small pox re-appeared in this city about the beginning of December last, after an absence of several years. About 30 persons have died of this loathsome disease.—Much public interest has been excited in order to put a stop to its ravages, by endeavouring to promote a general vaccination. For this purpose Ward meetings have been held throughout the city. Meetings of the inhabitants of the district of Southwark, and of the Northern Liberties, have also been called for the same valuable purpose.

The exertions of the Vaccine Society for vaccinating the poor at their own habitations, have been laudably increased; so that we may reasonably hope that an effectual stop will be put to this terrible disease, and that the present warning will serve to excite our fellow citizens in future, to a constant attention to the necessity of having their children vaccinated at an early age.

Native Epsom Salt.

Louisville, (Kentucky,) Feb. 12, 1816. It gives us much pleasure to inform our readers of the discovery of an extensive cave of native Epsom salt, or sulphate of magnesia, about thirty-six miles from this place, near the town of Corrydon, (Indiana Territory.) The cave is apparently inexhaustible; salt, of every variety of crystal, is arranged in all that fanciful splendor which decorates the grotto of Antiparos. This cave is the only specimen known of the pure salt in a solid form, except in Monroe county, (Virginia) where it is found under the surface of the earth. In Europe, and particularly in England, at the Epsom springs, which give name to the salt, it is obtained from water impregnated with it. We cordially hope that this native treasure will richly reward the chemical knowledge and enterprize of Doctors Burrel and Adams, of this town; who have the merit of analyzing and ascertaining this gentle and delightful cathartic. We have been promised some further particulars of the situation, dimensions, &c. of the cave, which will shortly be presented to the public.

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