Page images

Use of Sir Henry Englefield's Barometer.

When you arrive at the place of observation, place the stand on your foot, with the feet upwards; open the lid, by the lock and ketches; take out the cistern, with its gage, and put them in the right pocket, then turn the ketch that holds the bottom of the box to the sides; shut the lid, and secure it by one ketch; then open the back, and take out the tube which has the suspension piece and scale, which hold under the left arm, leaving the remainder of the tubes secure. Detach the lid and place the feet on the ground, spreading them as much as may be necessary; pull out the gimball at the top of the stand: take the bottle of mercury and unscrew the funnel; take out the cork, which put in the pocket, and replace the funnel. Now place the tube in the left hand with the thumb upwards about an inch from the open end; then take the body of the bottle in the right hand, the thumb resting on the funnel, and even with its small end. Now, holding the knuckle of the forefinger upwards, apply the end of the funnel to the aperture of the tube, the end of the thumb touching it at the same time. Now lift up the body of the bottle, the end of the thumb forming the centre of motion, and pour the mercury into the tube until it reaches to about a quarter of an inch of the end; then put down the bottle and put the cistern on to the end of the tube, pushing it as far as it will go. With the right hand take hold of the glass tube about an inch from the cistern, and with the left lift up the other end to an angle of about 45°, and you will ` perceive a large bubble of air passing up the tube and collecting all the small ones that were lodged there whilst pouring in the mercury. When the bubble has arrived at the top, gently reverse the position of the tube (turning it half round,) and it will collect the remaining air bubbles. This operation may be performed two or three times for greater security: Now, holding the tube in the left hand near the cistern, take it from the tube, and pour in a little more mercury until the tube is quite full, and replace the gage and cistern, pressing it firmly against

the end of the tube. Now hang the tube by the suspension piece in the gimball of the stand, and lifting up the gage with the left, pour mercury into the cistern until it forms a circle therein. (The bottle being taken care of either by putting it in a safe place, or replacing the cork.) Take hold of the glass tube about an inch above the cistern with the left, and with the right gently detach it a little from the tube with a screwing motion until the gage, which now floats on the mercury, coincides with the circle on the glass. Now set the scale to coincide with the inches between which the mercury stands, and read off carefully by the vernier in the usual way. The observation being completed and registered, in order to replace the barometer for a removal, take the tube from the gimball with the left hand, and taking hold of the cistern by the right, gently incline the tube until the mercury entirely fills the top, at which time push up the cistern against the open end of the tube, which may now be held vertical. Take hold of the tube with the left hand about a foot from the cistern, the forefinger pointing upwards, while the cistern rests against the arm just by the elbow, and resting on it. Then lift up the gage, to be held by the left hand; while with the right you take the bottle (divested of the cork and funnel), and apply the mouth of it and the end of the thumb to the edge of the open part of the cistern. Now, by gently inclining the glass tube, the mercury may be poured from the cistern into the bottle, which put down, and hold the tube in the left hand with the cistern upwards, which take from the tube. Now with the right hand apply the mouth of the bottle to the end of the glass tube, and turn it up so that the end may enter the bottle; hold the tube vertical, and the mercury will run out. Replace every thing as before.

ART. III. Description of the Apparatus, alluded to in the foregoing Paper, for bringing up Water from certain depths in the Sea.

[blocks in formation]

A is the bottle. B is a cylinder 12 inches long, and 1 in internal diameter; it is open below, but made tight above by a screw; a piston works in this tube, and at common atmospheric pressure includes a space of 6 inches between its internal surface and the top of the tube. A rod passes downwards from the under surface of the piston to the length of about 5 inches, and is then connected with the piece C by a VOL. V.


cross bar, passing through the aperture D, so that C is in fact a prolongation of the piston rod; and as D is an opening in the tube which extends nearly half way up it, a motion of the piston and the affixed part is allowed to that extent. E iş an arm sliding freely upon the cylinder. F is a screw fixed into it, which steadies, but does not bind the piece C. G is a click, or small lever, which is pressed by the bent spring on the outside against the edge of C and catches in the notches, when any one of them comes opposite to it. H is a small inclined plane which acts on the lower arm of the lever G. I is a piece which may be fixed on any part of C by the thumb screw, and when sufficiently raised, it comes in contact with the socket of the arm E. K is a lever attached to the plug of the cock; there is a spiral spring fixed round it at the head of the bottle, which constantly tends to throw it up and open the orifice. L is a second click or lever, which is pressed by a spring towards a horizontal position; its lower arm catches on a pin projecting from the end of the lever K, and keeps it down, the other end moves against the edge of the arm E. The cylinder is retained firmly in its place by two pieces passing from the top and bottom of the bottle. There is a square-headed screw in the bottom of the bottle, which, when removed, lets out the water : and the whole is slung in gimbles, to which the rope is made fast.-The action of the apparatus is as follows :-When the piston rises in the cylinder, it elevates the rod and the piece I; this coming against the socket of E, lifts the whole arm, and the inclined edge above acting on the end of the lever L, sets it off from the notch of the arm K, which rising, the bottle is opened, and water may enter. When the piston falls again, the click G catches in a notch on the edge of C, (these notches being made at proper intervals) and the arm E is in consequence brought down by means of the pin in its upper end; it depresses the lever K, and brings it within the click L, so that it is again retained its first position; and the moment this is done, the parts are so adapted to each other, that the inclined plane H, presses upon the end of the click G, and when it has descended a very little further, C is intirely liberated from the notch in which

If the

it had caught, and the arm E is left unattached. piston descends lower, it carries the piece C down with it, but does not affect any other part.-When the parts are adjusted to each other, a scale is marked off on C, the various points of which coincide with one, two, three, and more atmos pheres; and the piece I being set at these points, liberates the lever K at the moment those pressures are obtained; so that the whole being thrown into water, as it sinks, the pressure of the column of water above is exerted on the piston, and opens the bottle at the precise depth for which the piece I had been previously set.

The instrument was made under the direction of Sir H. Davy, by Mr. Newman, of Lisle-street.

ART IV. Extract of a Letter from John Davy, M. D. to Sir H. Davy.

Trincomale, Oct. 3, 1817.

My different excursions have been highly interesting. As soon as possible I shall give you a pretty minute account of the results of my observations. Now I must be very concise indeed. In July I went to the southern part of the island, and visited the districts of Matura and the Malagan-pattonIn the former, gems abound. I saw the natives at work in search of them in alluvial ground.─Here I ascertained that the native rock of the sapphire, ruby, cat's eye, and the different varieties of the zircon, is gneiss.-These minerals and cinnamon stone occur imbedded in this rock. In one place I found a great mass of rock, consisting almost entirely of zircon in a crystalline state, and deserving the name of the zircon rock. It is only a few miles distant from a rock called the cinnamon-stone rock, from its being chiefly composed of this mineral, in company with a little quartz and adularia. In the Malagan-patton, the most remarkable phenomena, and what I went chiefly to see, are the salt-lakes, the nature of which hitherto has been considered very mysterious, from the want of enquiry, which I was

« PreviousContinue »