nips. It was remembered by some farmers that this was the fly which prevailed in the year 1818, and which was followed by the caterpillars known by the name of the blacks. The eggs being deposited by the perfect insect in the leaf of the plant, the black caterpillar or turnip-pest speedily makes its appearance, feeding on the soft portions of the leaves of the turnips and leaving the fibres untouched; and finally, casting its black skin and assuming one of a more slaty or grey colour, it buries itself in the earth. Lodged there, it forms for itself, from the soil, a strong oval cocoon; from which some of the earlier broods pass almost immediately into the perfect state, filled with ova, and ready quickly to supply another generation of destroyers. So complete and so rapid was the destruction in some instances, that a whole field was found, in two or three days, to present only an assemblage of skeletonized leaves; and this too when the turnips had attained a considerable size. The insect whose proceedings have been thus briefly noticed, belongs to the Hymenopterous family Tenthredinida; it is the Athalia Centifolia, a species first noticed by Panzer. Mr. Yarrell describes the perfect insect and the caterpillar; and then recurs to the damage effected by the latter. By their repeated broods the devastation was continued for so long a time that even the third sowing did not in all cases escape destruction; and it was not until the occurrence of the heavy rains in September, terminating the unusually dry summer, that the mischief ceased. The destruction of the leaves caused, in most instances, the loss of the root also; and where the leaves suffered from the attacks of the black caterpillar, but not sufficiently to occasion the death of the plant, the turnip itself became pithy and of little value. It has become necessary, Mr. Yarrell states, to import the root largely from the Continent to supply the deficiency of the home crop. The remedial measures adopted on a former visitation were the turning into the infested fields of a large number of ducks, who greedily devoured the caterpillars as they were brushed from the leaves by a boy with a long pole; the passing of a heavy roller over the ground at night, when the caterpillars were at their feed; and the strewing of quick lime by broad cast over the fields, renewing it as often as it was dispersed by the wind. The latter mode was generally considered as the most effectual preservative. PROCEEDINGS AT THE FRIDAY-EVENING MEETINGS OF THE ROYAL INSTITUTION. Jan. 22, 1836.-Mr. Faraday on silicified plants and fossils, and the proposed theories of silicification. Jan. 29.-Dr. Ritchie. A view of the differential and integral calculus. Feb. 5.-Mr. Brande on the manufacture of paper-bangings. Feb. 12.-Dr. Grant on the structure of fishes, considered with reference to their aqueous element. Feb. 19. Mr. Faraday on the magnetism of metals as a general character (see page 177). Feb. 26.-Dr. Lardner on steam communication with India. March 4.—Mr. Fox on a mode of laying out and working oblique or askew bridges. (See p. 299 of the present Number.) March 11. Dr. Arnott on warming and ventilating buildings. March 18-Mr. Wheatstone on the means of investigating the structure of crystalline bodies by their sonorous vibrations. LXV. Intelligence and Miscellaneous Articles. ON THE ATTRACTIVE AND REPULSIVE FORCES OF MAGNETS AT VERY SMALL DISTANCES. Note applicable to the Correspondence between Professor Ritchie and Mr. R. W. Fox, (see our last four Numbers,) on the attractive and repulsive forces of magnets at very small distances. Extracted by a Correspondent from a paper by W. Snow Harris, Esq., F.R.S., in the Trans. R.S. Edinburgh, 1831; dated July 1, 1827. " N the following table are the results of a series of experiments with the attracting and repelling poles. The magnets em-ployed are indicated by the letters a, b, c, d, e, their dimensions being as follows: a, A small cylindrical magnet 2 inches long, 0.2 of an inch in diameter, and similar in every respect to the suspended magnet T [on which its force was exerted]. b, 4.5 inches long, and 0.4 of an inch square. c, 7.0 inches in length, and 0.7 of an inch diameter. d, 9.0 inches long, 0.8 of an inch wide, and 0.3 of an inch thick. e, 14.0 inches long, 10 inch wide, and 0.5 of an inch thick. D signifies the distance; whilst the letters a, b, c, d, e are placed over the respective forces." "These experimental results are quite consistent with the operations of the inductive influence [before explained]. We immediately perceive, by referring to the attractive forces, that the law of the in • At these distances the repulsive force was superseded by attraction. verse square of the distance is manifest through all the approximations, except a few of the last, the occasional irregularities observed being very inconsiderable; so that when the magnets are very nearly approximated in relation to their respective intensities, the increments in the forces begin to decline, a circumstance of considerable importance in our endeavours to investigate the laws of magnetic attraction; for it may be supposed that the inductive influence which thus begins to vary, may at last so far vanish, even before contact, that the absolute force, at near approximations, may in some instances, as already stated, be in an inverse SIMPLE RATIO OF THE DISTANCE*, and which was observed to happen with the bars marked d and e. For although the cylindrical counterpoise employed in these experiments did not admit of the forces being examined at nearer approximations than those marked in the table, yet by substituting one of large dimensions the forces may be carried on nearly up to the point of contact, so as to be estimated in terms of the preceding progression, since the degrees of attraction may be always compared and valued in grains of absolute weight." "In the following table are the results of the experiments so continued with the magnets d and e; the counterpoise being 10 inch in diameter, 1° of attraction corresponding to 10° of the former, and being equal to two grains of absolute weight:" "It may be perceived in this table, that the corresponding forces at near approximations, do not materially vary from a simple inverse ratio of the distance.” "This deviation from the law of the inverse square of the distance observed in all the near approximations of the magnets may happen either in consequence of the distant polarities having passed a certain limit, or otherwise from the inductive action not going on with the same freedom at some point approaching saturation. The latter would seem to be extremely probable; for it has been already shown, that when two dissimilar polarities are opposed to each other, their free action becomes more or less neutralized."--Trans. of Royal Society of Edinburgh, vol. xi. p. 310-312. W. J. H. ON THE AURORA OF THE 18TH NOVEMBER LAST. Communicated by Professor Rigaud. During the beautiful aurora which took place on the 18th of last November, it is remarkable that Mr. Sturgeon was not able to see any of its light excepting in the north. Dr. Robinson, in the last number of the Phil. Mag. (p. 236.), has drawn an important conclusion from this circumstance: it may be right, therefore, to state • The Italics and capitals in this passage are our Correspondent's.-EDIT. that in Oxford the streams of light rose and continued for a considerable time to pass far beyond the zenith. A little, also, after nine o'clock, an arch like a long, luminous, narrow cloud extended from about the E.N.E. or N.E. by E. nearly across the heavens. It appeared to have an altitude of about 60° where it cut the southern meridian. The approximation of this situation to that of the magnetic equator would have given great value to this phænomenon, if the arch had been more definite in its form, and the place could have been more accurately determined in which itreached the horizon; but this last circumstance could only be collected from its passing near Jupiter. The Oxford Herald of the 21st mentioned that this arch had been also observed at Banbury. NOTE ON MR. ATKINSON'S PAPER INSERTED IN THE LAST NUMBER OF OUR JOURNAL, PAGE 188. We regret that we should have given currency to a paragraph in the above-mentioned paper, which seems to imply a degree of negligence on the part of the Assistant Secretary at the Royal Society's, whose duty it is to make and record the Meteorological Observations there. If Mr. Atkinson had taken the precaution to make inquiries at the apartments of the Royal Society, he would have found that the anomalies and apparent errors to which he alludes are not owing to want of care and attention on the part of the Assistant Secretary, but to the position in which the instruments are placed; which position, although evidently not a good one, is the best which the locale of the Society presents. The instruments are all of the best kind, and of superior accuracy and workmanship.-EDIT. METEOROLOGICAL OBSERVATIONS FOR FEBRUARY 1836. Chiswick-February 1. Slightly overcast : fine. 2. Hazy rain: baro5. Hazy and cold. 6. Very fine. 7. Drizzly: cloudy and mild. 8, 9. Overcast. 10. Showery. 11. Clear and cold. 12. Cold and windy. 13. Sharp frost : fine. 14. Fine. 15. Clear and frosty. 17, 18. Clear, cold and windy. 19, 20. Sharp frost: fine but cold. 21. Frosty clear. : 22, 23. Overcast. 24. Overcast : fine. 25. Frosty: fine. 26. Sleet; rain. 27. Drizzly. 28. Hazy cloudy and fine. meter extremely low. 3. Rain. 4. Wet and stormy. : 16. Frosty. 29. Overcast. During the first three days of the month the barometer fell remarkably low, and particularly on the 2nd, on which day it was lower than it has probably been for many years in the vicinity of London. The fall of rain was not remarkably great, nor was the temperature at nights below freezing; but in the country the fall of snow was, at the same time, unusually deep, and the storm so excessively violent that the mails were in many instances obstructed in consequence. 2. Fine: snow Boston.-February 1. Cloudy and stormy: rain early A.M. P.M. with rain. 3. Cloudy: rain early A.M. 4. Cloudy and stormy: rain 6. Fine. 7. Cloudy: rain early A.M.; rain P.M. 9. Fine. 10. Rain: rain P.M. 11. Fine and stormy. 14. Cloudy. 15. Fine. 16. Cloudy. 17. Stormy: 18. Stormy. 19, 20. Fine. 26. Cloudy: rain P.M. P.M. 5. Cloudy. 21. Cloudy. 22. Fine. 27. Cloudy. 28. Cloudy: Meteorological Observations made at the Apartments of the Royal Society by the Assistant Secretary; by Mr. THOMPSON at the Garden of the Horticultural Society at Chiswick, near London; and by Mr. VEALL at Boston. Days of 1836. Chiswick. Boston. London: 84 A.M. Roy. Soc. 9 A.M. Chisw. Bost. Max. Max. Min.) 30-231 30-474 30-450 30-05 30-2 26.5 36.2 39 19 31 N. E. calm 25 ... ... 30-180 30-407 30-218 29-92 29.1 25.3 38.3 42 28 34.5 NW. SW. calm 25 39.2 27.8 37.7❘ 45 28 36 SSW. SW. calm 30 34.2 43.2 43 26 40 SSW. SW. calm 33 |