500 PHILOSOPHICAL TRANSACTIONS. [aNNO 1748. 



1745 May 14 17° 20' 1746. Feb. 24 17" 30' 



16. .,17 15 1747. Dec. 19 17 40 



Dec. 18 17 25+ Jan. 4 17 40 — 



The inclination of the dipping-needle was during the same time about 73f 

 degrees. 



As the variation of the needle at London has not been regularly published 

 from time to time in the Phil. Trans., it may not be improper to take notice 

 here, that according to the best observations extant, and which were made by 

 persons of great skill and exactness, the needle at London declined to the east- 

 ward 11° 15' in the year 1580. In 1657 there was no variation, the needle then 

 pointing due north. In 1672 the variation was observed by the late Dr. Halley 

 2° 30' towards the west, and in 1692 6" o'. Towards the beginning of the year 

 1723, it was found by Mr. Graham, from the medium of a vast number of ob- 

 servations, to be then 14° 17' the same way. So that, during the course of 

 167 years, elapsed since the year 1580, to the end of the last year 1747, the 

 magnetic needle at London has moved to the westward 28° 55'. See before N° 

 148, and N" 383 of the Phil. Trans. 



Account of the Cornel-Caterpillar.* By the Rev . Philip Skelton. N°487, p. 281. 



In the beginning of May 1737, the warmest season that any one remembers, 

 the cornel-trees, of which we have a good number about Monaghan, appeared 

 almost covered with small caterpillars, of a duskish green, resembling in colour 

 the bark of the tree, though a few, considerably larger than the rest, were yel- 

 low. These worms were employed partly in feeding on the leaves of the cornel, 

 which was their only nourishment, and partly in crawling over the bark of the 

 tree. As they crawled, they left each a fine thread, scarcely visible to the naked 

 eye, sticking to the bark. These threads, being almost infinitely multiplied by 

 the inconceivable number of worms employed in the work, formed the web, in 

 which the threads are not interwoven, but cohere by some roughness or gluti- 

 nous quality. 



By the end of May there was not a leaf to be seen on any of the cornels, ex- 

 cepting a few, reserved for a very curious purpose, mentioned presently. But 

 the worms, in stead of the green cloathing they robbed those trees of, gave them 

 one of white, so entire, that it covered the whole bark, from the ground to the 

 points of the slenderest twigs, and of so pure and glossy a colour, that the whole 

 tree showed in the sun as if cased in burnished silver. The web was so strong, 

 that if one disengaged it from the tree, near the root, one might have stripped it 

 from the trunk, the branches, and the twigs, at one pull. As soon as the worms 



* The insects here described are the larvae or caterpillars of the Pialana Evonymella, Lixin. 



