Page:Madras Journal of Literature and Science, series 1, volume 6 (1837).djvu/359

1837.]

my communication respecting the Self-registering barometer published in No. 16 of the Journal, page 68, I mentioned with respect to the feat which regulates the motion of the tube, that, "if this float be sufficiently large to buoy up the tube, the balance part of the apparatus may be laid aside altogether, and the weight below the cistern, acting on the principle of ballast, will preserve the tube in the perpendicular." I have fitted up a barometer on this principle. It has been in operation the last two days, and I have the pleasure to state that it proves most satisfactorily the correctness of the principle stated in the above quotation. I fear that a sketch of a plan of a barometer on this principle, could not be lithographed in time for the issue of No. 17, of the Journal now due, otherwise would send one. In the mean time, however, it will be satisfactory to those who wish well to the advancement of meteorology, to be informed that a barometer, of so simple a construction as the one alluded to, can be made that will, with scientific correctness, make a perpetual record of the varying pressure of the atmosphere.

In fitting up the barometer referred to, I purposed merely to test the correctness of the principle, without reference to accuracy in the details of construction—in other words simply to ascertain whether the instrument would work. The tube portion consisted of a four-ounce glass stopper vial, by way of expanded top, cemented by means of bees' wax to a common barometer tube, the closed end of which was previously cut off. Presuming that those who interest themselves in meteorology would desire to test this principle, in the like easy manner, I will mention somewhat in detail the fitting up of the instrument, as otherwise one or two failures may occur before success be attained. In order to cement the vial and tube together, the mouth of the former and one end of the latter ought to be coated with melted wax—when cold, the tube is to be pushed about half an inch into the mouth of the vial and retained perpendicularly—then about four inches of the tube and one inch of the vial are to be coated with wax—applied in the fashion of paint—and when one is cold, successive coats are to be applied, until a body of wax has accumulated, sufficiently strong to keep the vial and tube firmly attached. It is essential to apply the wax coat after coat in the manner stated— as I found the applying it in the manner of casting did not make an air-tight joint. When the wax is