water in grains troy.

tude in inches.

Corrected weight of Corresponding alti-Corrected weight of Corresponding alti

water in grains troy.

tude in inches.

An Example showing the Use of the Tables.

Suppose the weight of the water in the gauge corrected by subtracting the weight of the gauge, to be 20 lb. 5 ounces avoirdupois, required the height or number of inches of rain?

2. If the weight, reduced to grains, be found in Table 3, the corresponding height will be found opposite to it in the adjoining column; but as, in this example, it is not, take the nearest, less, number to it from the table, and subtract it from the weight of the water, marking the corresponding height in inches, &c. Enter the table a second time with the difference and take the nearest less number to it, together with its correspondent height, which subtract from the difference, and with the remainder enter the table again, if necessary, thus,

The nearest number in the table, less than 142406-25, which must be subtracted, is..

126262.5

500

Difference.

16143-75

The next number in the table, less than the

difference, is...

15151.5

0.60

which, when subtracted, leaves the remainder.

992.25

The nearest number corresponding to the remainder in the table, is.

The sum of the corresponding heights gives...... Inches 5.64

It is obviously not necessary to be restricted to either the form or the size of the above described gauge. If the cylindrical form be thought to possess any advantages over that of a square prism, it is easy to find the diameter of a circle whose area shall be equal to 100 square inches, by the well-known rule, viz. d =

a 7854

where d represents the diameter, a the area, and 7854 the area of a circle, whose diameter is unity. If any other size should be thought more convenient, as, for instance, one whose area is only half of that of the above-described gauge, the same rule, if cylindrical, will give the corresponding diameter, or if a square-mouthed one be preferred, the side of the square is obtained by extracting the square root of fifty. But it must be remembered that whatever relation the area we pitch upon may bear to 100 square inches, the same relation will subsist between the final result, and that which is given by the tables: thus if the area of the gauge be fifty square inches, as this is the half of 100, we must take half the sum of the tabular heights for the true altitude.

It is not necessary to be very particular in the choice of a balance; a pair of good common scales will answer, with true weights, either troy or avoirdupois. The gauge may be made of

tin, or sheet iron painted or japanned, but copper is more durable. The area of the funnel, and that of the top of the body part, are the only parts that need attention in the construction. These ought to be made tolerably exact. A strong hoop should be fixed around them on the outside to preserve their figure true.

In every operation. of weighing, the weight of the gauge, moistened in the inside, must be deducted from the gross weight; the remainder is the corrected weight of the water with which the tables must be entered.

In the case of hail, snow, sleet, or frozen water, being in the gauge, it is not necessary to melt its contents into water, as the changes effected by temperature and pressure make no difference in the weight.

The use of scales and weights may be dispensed with, by substituting a steelyard, so constructed that the movable weight on its arm might indicate by its position, not the weight, but the inches and decimal parts of its corresponding altitude, without reference to the tables, and without calculation.

The advantages of this method of finding the quantity of rain in linear inches of altitude, will be appreciated by adverting to the circumstance of our having a tangible quantity, as an unerring guide to that which is nearly imperceptible. Twenty-five grains and a half, a sensible quantity in a good balance, pointing out the difficultly visible division of the Toth part of an inch. Suppose the problem reversed; that the cubical contents of the water, or its weight, were required, from the observed altitude. The chances of error would all be against the accuracy of such a determination. The difficulties of the task, independently of the aforementioned causes of variation, would evidently be insurmountable.

I had a gauge constructed on this principle, twelve or fourteen years ago, for my friend Dr. Akerly, who informs me that it answered the end extremely well. This testimony in its favour is not among the least of those considerations that have induced me to make it more generally known.

Fig. 1.

Fig. 2.

10. Incives.

G.C.

Fig. 1, represents the rain gauge in perspective.
Fig. 2, is a vertical section.

G the body of the gauge, F its funnel, L the lid or cover, v the valve, hinged to the lower orifice of the funnel, s the spring to close the valve, w a wire to conduct the drainings of the funnel into the body of the gauge.

ARTICLE VIII.

On Baryto-Calcite. By H. J. Brooke, FRS. &c.

(To the Editors of the Annals of Philosophy.)

GENTLEMEN, July 15, 1824. MR. BROUGHTON, before he left London, favoured me with specimens of a mineral from Cumberland which had been considered to be carbonate of barytes, but it was very evident that the crystals did not resemble the ordinary figures of carbonate of barytes, and the substance was, therefore, regarded by Mr. Broughton as something new.

P

The external surface of the specimens is coated with sulphate of barytes; but the internal mass frequently contains cavities which are lined, and nearly filled with crystals. The primary form of these is an oblique rhombic prism, as shown in the annexed figure, the cleavage being parallel to the planes P, M, and M.

All the crystals I have seen are modified on some of the edges and angles, and are lengthened in the direction of the edges of the modifying planes, presenting the character of prisms terminated by the bright planes P, a, M, and h, of the figure. The modifying planes are, however, so numerous, irregular and dull in my specimens, that I have not obtained sufficiently good or corresponding measurements to enable me to ascertain their character, and they are, therefore, omitted in the drawing.

The mineral is translucent with a slight tinge of a yellowishbrown colour.

Its lustre rather more waxy than carbonate of barytes. Its hardness is between that of carbonate and fluate of lime. Its specific gravity, as ascertained by Mr. Children, is 3.66. The name baryto-calcite has been given from its chemical composition, as ascertained by Mr. Children.

* The mean specific gravity of carbonate of barytes and carbonate of lime is 3.5.-C

Chemical Examination of the Baryto-Calcite. By J. G. Children, FRS. &c.

With the blowpipe this mineral exhibits the following cha

racters.

In the forceps, in the oxidating flame, it neither fuses nor decrepitates; its surface becomes green, and the point of the flame, beyond the assay, assumes a light greenish-yellow colour. In the reducing flame the superficial green colour disappears. The assay, after being ignited, browns moistened turmeric paper. Heated to redness, in a glass tube, it merely gives off a little

moisture.

By heat the assay becomes strongly phosphorescent, shining with a pale-yellow light, very similar to that of the common glow-worm.

With soda, on the platina wire, in the oxidating flame, it gives a bluish-green opaque mass. In the reducing flame the green colour is discharged.

With borax, in the oxidating flame, dissolves readily into a perfectly diaphanous globule of a beautiful light amethystine colour. The globule retains its transparency in the reducing flame, but entirely loses its colour.

With salt of phosphorus, dissolves very readily; the globule is perfectly transparent, and in the oxidating flame yellow while hot; when cold, colourless. In the reducing flame the globule is colourless, and, while hot, transparent; when cold, its transparency is slightly disturbed.

Analysis.

To ascertain the proportions of its elements, I dissolved the mineral in muriatic acid, diluted the solution very largely with distilled water, and precipitated the barytes by sulphate of ammonia; boiled the precipitate to take up any sulphate of lime that might have been thrown down, filtered, and washed the precipitate, till the washings ceased to give any cloud with oxalate of ammonia, adding the washings to the solution from which the sulphate of barytes had been separated. The solution, being first reduced by evaporation, was then boiled with a solution of carbonate of potash, which threw down the lime in the state in which it originally existed in the mineral. Treated in this manner, 20 grs. gave

Grains.

Sulphate of barytes 15.55 grs. carbonate of barytes 13.18 Carbonate of lime.

6.72

19.90

A minute portion, not exceeding one or two-tenths of a grain,