THE UNITED STATES' TRAMSIT OF VENUS EXPEDITION.

New Zealand Herald, Volume XIX, Issue 6566, 2 December 1882, Page 6

THE UNITED STATES' TRAMSIT OF VENUS EXPEDITION.

PEXDULUM EXPERIMENTS. Mr. KmviN Smith, tin- chief of the United States' Transit of Yomia r» r V at Auckland, would seem to have his hands pretty lull of work. Kot o;uy is >>, m carrying out the tnaiiv .lelails reMii.K to the coming transit of Venus, but h, is daily carrying meuts. 1,,;n ,"-, .; Ü b ;;,, , 10110 \ n different r?c E s!tv of th, cart!, at various places by n ,. IM of the pendulum. The north. .» hem?-l»hcre hns been more examined ,y thia Xod the southern one, 1,1 which is our adopted l-.ome. Indeed, up to the prrsent time no pendulum work has been none in New Sn.l* In Sydney, some work of th.s kind has been accomplished, bit it is eenerallv reg.irded as of a doubtful character ind it is Mr. Smith's intention to proceed there after leaving Auckland to carry out a course of experiments ; thence to Singapore, and thence to Tokio, .lapan. where work of this class will also be undertaken lor the first time. Not only is the pendulum used for determining the gravity or weight of the earth but it is also found to be a very accurate instrumental method of determining the absolute figure of the earth. Many British officers have spent largo portions of their lives in carrying out such tedious, though important, work as the use 01 the pendulum demands. The late Captain SSabine was a'i enthusiastic worker in this field of science, and large portions of India were visittd by him for the purpose of perfectiu" our knowledge of the physical figure and constitution of the earth so far as the pendulum could throw light. In the early part of the present centurv a ereat deal of attention was pven as to "the best form of pendulum, and tnc conditions under whi=h it could best be used. It was reserved to Captain Henry Kater to design the form which has since been almost everywhere uped knnwn as KatT's Invariable Pendulum. The shaft of the pendulum is of brass, and is suspended in a large iron cylinder, which, being covered with a glass cap, is exhausted of air by an air pump. The swinging of the pendulum is thus carried on under the most ravourable conditions, free from the pressure of atmospheric air, anil resting upon a knife edec the resistance caused by friction is reduced to a minimum. In the lower part of the cylinder in which the pendulum swings, in n vacuum, are placed openings covered with class which aflbrd the observer an opportunity Of making the record as the pendulum swings in front of a large, and marked, and illumine ted pundulnminconnection with cIoIL work. ThMuitaMHty of Rater's design w.-w so -renerallv approved, that thirteen exact Sopies of it were made by Mr. Jones, a matheniatic.il instrument maker Lomion, from ISIS to IS2I. These have been d.stnbuted to different parts of the world ; a number of them, however, have at present been lost si"ht of. The other copies at prosent known have all been more or less altered since they were first made, either by grinding the knife edge upon ■ which the pendulum rests, or some other way, except No 4 This is one of the three now in the possession of Mr. Smith; the Others of which he has charge, being known as f>o. 0 and No. 11. The two first mentioned arc the property of the Royal Society, London, and No. 11 "belongs to the British Admiralty. No 4 was at one time owned by the Admiralty but lias been for several years the property of the Royal Society. These instruments have been lent to the United States Government and Geodetic [survey Department (of which Mr. Smith is an officer), and Mr. Smith's visit to INew Zealand was taken advantage of to have them .swung in Auckland. It need not be pointed out the importance Of having work of this kind done in different parts of the world with the same instruments unaltered in any was'. S ? far as ia known, the No. 4 copy of Rater's is the only one of the thirteen made that can lay claim to this distinction. The apparatus connected with the pendulum work is fitted op in the old blockhouse in the Domain. The room in -which it is erected is completely darkened, and all precautions are taken to exclude currents of air however feeble. To pec-are perfect steadiness, a large portion of the flooring in the room has been cut away, and a huge block of concrete firmly embedded in the ground. Upon this block, separated on all sides by several inches from the ■wooden floor, is erected the framework in •which the pendulum is swinging. In the opening between the concrete block and the edge of the cut floor is stretched ail round several folds of cotton cloth, thus preventing an inflow of air from the outside, by that •which has sufficient flexibility to prevent the least jar being communhated to the supporting block by those walking on the floor. Every care is taken by sfr. Smith to secure correct readings, and Professor Pritchett, of St. Louis University, is as indefatigable in making the readings. Of course it does not require to be stated that all the work done in this room is done by means of artificial light. A brief account of the career of these historical scientific instruments may not be void of interest. - No. 4 was originally the property of Captain Sabine, and was used by him chiefly in India, from IS2I to 1524; by .Ronald in 1525 ; by Fallows in 1529 ; by Stewart and Lowey in ISCS ; by Basevi in 1565 to IS7I ; by Herschell in 1873 ; and by Herschell again in 18S1 and 18S2. As previously stated, it was purchased by the Admiralty, but is now the property of the Royal Society. The history of No. 6 is unknown until 1554, though it is known to have been made in IS2I. In 1554 it was used by Sir George Airy ; in 1565 by Stewart and Lowey ; from 1865 to IS7I by Basevi; in 1873 by Herschell ;• and also by Herschell again in ISBI and ISS2. No. 11 was used by Foster in IS2S to 1831 ; by Bailie in 1533 ; by McLean in 1539, and by Bailie again in IS4O ; and subsequently by Herschell in ISBI and ISS2. The two first named were used in connection with the great survey of India from 1565 to 1574. On their return to England in that year they were swung at Aden, and subsequently at Ismailia. In 1881 Herschell, after their long residence abroad, had them swung again at Kew, Greenwich, and Langham, to test whether any change had taken place in them since leaving Britain. In the present year he had them swung at Washington, and at Hoboken, which is frequently called the New York station. Then they were handed over to the United States Coast and Geodetic Survey, and are now here tm charge of Mr. Smith. It is pleasant to see the different members of the AngloSaxon family manifesting such a friendly feeling to each other, and it h to be hoped that this friendly feeling in science will soon be manifested in an equally expressive manner politically by a federation of the English-speaking communities all over the world.