The places of the Sun and Moon have been taken from the Nautical Almanac, those of Mercury from Lindenau’s Tables, and those of the other Planets from Schumacher’s Ephemeris.——The sign + denotes the motion in A. R. to be direct; the sign −, retrograde. The sign + denotes the motion in N. P. D. to be towards the South; the sign − towards the North.——None of the preceding Conjunctions will prove to be an Eclipse or Occultation visible at Greenwich. [p452]
| Apparent Distance of Jupiter’s Satellites from Jupiter’s Centre, at his Conjunctions in A. R. with the Moon. | |||
|---|---|---|---|
| Date. | Satellite. | Distance. | |
| 1828. | ′ ″ | ||
| January 11 | I. | 1 14 | East |
| II. | 0 51 | —— | |
| III. | 4 16 | West | |
| IV. | 2 21 | —— | |
| February 7 | I. | 1 6 | West |
| II. | 2 40 | East | |
| III. | 2 16 | West | |
| IV. | 4 27 | —— | |
| March 6 | I. | 1 51 | East |
| II. | 2 24 | West | |
| III. | 3 14 | East | |
| IV. | 8 44 | —— | |
| April 2 | I. | 1 44 | West |
| II. | 0 15 | ——A | |
| III. | 4 58 | East | |
| IV. | 7 30 | West | |
| 29 | I. | 0 14 | WestB |
| II. | 2 51 | East | |
| III. | 0 32 | West | |
| IV. | 1 6 | East | |
| May 26 | I. | 1 44 | East |
| II. | 3 8 | West | |
| III. | 5 15 | —— | |
| IV. | 6 38 | East | |
| June 22 | I. | 1 59 | West |
| II. | 0 4 | EastC | |
| III. | 3 10 | West | |
| IV. | 8 56 | —— | |
| July 20 | I. | 1 51 | East |
| II. | 2 50 | —— | |
| III. | 1 55 | —— | |
| IV. | 4 51 | —— | |
| August 16 | I. | 1 43 | West |
| II. | 1 12 | —— | |
| III. | 4 21 | East | |
| IV. | 1 53 | —— | |
A: On Jupiter’s disk. B: Eclipsed. C: On Jupiters disk. These Configurations have been computed from De Lambre’s Tables.[p453] | |||
MISCELLANEOUS INTELLIGENCE.
I. MECHANICAL SCIENCE. [◊]
1. On the Adhesion of Screws.
“The screws I used were about two inches in length, 0.22 diameter at the exterior of the threads, 0.15 diameter at the bottom, the depth of the worm or thread being 0.035, and the number of threads in one inch = 12. They were passed through pieces of wood exactly half an inch in thickness, and drawn out by the weights specified in the following table:
| Dry beech | 460 | pounds |
| Do. Do. | 790 | |
| Dry sound ash | 790 | |
| Dry oak | 760 | |
| Dry mahogany | 770 | |
| Dry elm | 655 | |
| Dry sycamore | 830 |
“The weights were supported about two minutes before the screws were extracted.
“I have also found the force required to draw similar screws out of deal and the softer woods about half the above.
“From which we may infer as a rule to estimate the full force of adhesion, in hard wood . . . 200.000 d δ t = f, and in soft wood . . . 100.000 d δ t = f, d being the diameter of the screw; δ the depth of the worm or thread; and t the thickness of the wood into which it is forced;—all in inches; f being the force in pounds to extract the same.” We may, from the above experiments, observe the approximation to perfection in the art of screw making; for had the screw been greater in diameter, there would have been a waste of material, or had it been less, it would not have been sufficiently strong, which may be proved as follows: the cohesion of wrought iron has been found, from a number of experiments, to be about 43000 lbs. per cylindrical inch; and as the smallest diameter of screw used in my experiment was 0.15, it would have been torn asunder by a force of about 968 lbs.; or if the hard wood had been about 58 of an inch thick into which it had been screwed, the screw would have been broken instead of forcing its passage out of the wood.—Phil. Mag. N. S. ii. 291.