INTRODUCTION. DURING the year 1862, the Meteorological observations were under the charge of Mr. John Lucas, who took the general management of all the operations connected with this department of the Observatory. He took general charge of the Meteoro-Photographic instruments, and of the preparation of the photographic paper, and made such observations with the ordinary instruments as are necessary for verifying or correcting the assumed zeros of the Photographic Registers. He was also charged generally with the reduction of the observations, but the greater portion of the discussions relating to the diurnal inequalities of the meteorological elements has been performed, as in former years, by myself. Ordinary Instruments. The Instruments during the year 1862 were identically the same as in the preceding year; but it is desirable to repeat the account of them which has been given in preceding volumes. They are the following: 1. A Barometer by Newman, placed in the N. E. corner of the Circle Room, with its cistern at an elevation of 2 feet above the floor. The tube of this Barometer is 0.528 inches in diameter. The zero of the graduated scale is marked by the apex of an inverted ivory cone, to which the surface of the mercury in the reservoir is adjusted before reading: the vernier will read to 002 of an inch. The correction for capillarity is +oin.003. It was mentioned in the Introduction to the Meteorological Observations for 1861, that the ring carrying the index to the vernier, was repaired at the commencement of 1862, and that the error arising from this cause, if any, must be very small. The old Barometer by Bird, used till 1838, is in the Quadrant Room. 2. A Dry Bulb Thermometer, N. 230, by Negretti and Zambra, used as the standard. 3. A Wet Bulb Thermometer, No. 230, by ditto. 4. A Dry Maximum and a Dry Minimum Thermometer, Nos. 1056 and 652, by ditto. 5. A Wet Bulb Maximum and a Wet Bulb Minimum Thermometer, No. 1055 and 740, by the same makers. These Thermometers are all placed on one frame, about four and a half feet above the ground, within a penthouse situated on the north [B] RADCLIFFE OBSERVATIONS, 1862. side of the Observatory, outside the Circle Room, and at a distance of about six feet from the wall. The penthouse is so constructed of open work as to allow a perfectly free passage of air, and, at the same time, to afford a good protection to the Instruments from storms and rain. All these Instruments were compared by Mr. Glaisher with his standard, previously to their being sent to Oxford, and their corrections were found to be small. 6. A Sky-radiation Thermometer, placed on the ground near the frame carrying the other Thermometers in the early part of the year (as in preceding years), but afterwards removed to a more exposed situation. 7. A Solar-radiation Thermometer, with blackened bulb, placed in a niche in the south wall of the west wing of the Observatory, outside the Transit Room. 8. A Self-registering Max. and Min. Thermometer by Troughton and Simms, placed on a frame at the top of the tower in April 1862. In connexion with the Barometer it may be mentioned, that the height of the cistern above the mean level of the sea has been for some years assumed by Mr. Johnson to be 210 feet, by comparison of the mean yearly pressures with that given by Kaemtz as the pressure at the mean level of the sea, namely, 29.975 for latitudes near the Oxford parallel. The height of 210 feet is assumed in the reductions of 1862. This assumption (210 feet) is essentially confirmed by the spiritlevellings taken in connexion with the Ordnance Survey*. At page 237 of the work of which the title is given beneath, it is stated that "a mark on plinth in wall opposite the Observatory, 158 feet above the surface, is 209.686 feet above the mean level of the sea at Liverpool." The surface of the ground, therefore, at this point (that is, at a point in the east wall of the grounds of the Observatory) is 2081 feet above the sea level, and, assuming that there is no variation of level between this point and the ground outside the Circle Room in which the Barometer is placed, this will give about 212 feet for the height of the cistern. 9. Four Rain-gauges. One was, in the early part of the year, placed on a slab of stone on a level with the ground on the south side of the Observatory, and at some little distance from it; and the second on the leads above the east wing of the Observatory, at an elevation of 22 feet. On May 20, the former was removed to a more exposed situation on the grass plot north of the * Abstracts of the Principal Lines of Spirit-Levelling in England and Wales. By Colonel Sir Henry James, R. E., F. R.S. London, 1861. Observatory; and the latter, on Feb. 7, was raised to the height of 24 feet that it might be less sheltered. Some trifling alterations were, at the same time, made in it, to prevent evaporation. It (the latter) communicates with a tube leading to a receiving vessel in the north-west corner of the Quadrant Room. The rain is poured into a graduated glass vessel of one inch diameter, for the purpose of being measured. A little evaporation may take place in the gauge on the ground, but, as the rain is measured every day, no sensible loss is experienced. Of the two others, the first is at an elevation of 22 feet, on the small building formerly used for mounting the Anemograph; and the second, on the top of the tower. Photographic Instruments. In these there has been no organic change since the preceding year. They consist of the following: 1. A Barograph, placed in a small north room between the Transit Room and the Circle Room, for a description of which, together with an account of the method of deducing the value of the scale, &c., &c., the volumes for 1854 and 1855 of the Radcliffe Observations may be consulted. The following Table gives the results of the comparison of the mean values of the Register at 2h, 10, and 22h of each day, with the mean readings of the Barometer at the same hours, corrected for capillarity and reduced to 32°. |