CONTENTS. xbc 



JANUARY 1799. 



Engravings of the following Objcfts: i. A New Inftrument for ruling parallel 

 Lines for the Ufe of Engravers : and, 2. Mr. Cavendifh's Apparatus for mea- 

 furing the mutual Gravitation of Bodies, and afcertaining the Denfity of the 

 Earth. 



I. Defcription of a New Inftrument for drawing equidillant and other parallel 

 Lines, with great Accuracy and Expedition, intended principally for the Ufe of 

 Engravers j with Specimens of its Performance. By W. N. p. 429 



The inftrument confifts of two flat rulers, one of which cojifines tlie plate, and the other is made to 

 fiiift through fmall intervals by means of a fcrew and gear, while it conftantly preferves its pa- 

 rallelifm. 



IL Memoir on the Climate of Ireland. By the Rev. William Hamilton, of 

 Favet, in the County of Donegal ; late Fellow of Trinity College, Dublin; 

 M.R.LA. Correfponding Member of the Royal Society of Edinburgh, &c. 

 (Concluded from page 386, Vol. II.) — — P- 43i 



General effefts of the weftern tempefts on the climate of Ireland. The fummers are rendered 

 colder, and the winters milder. — This equable temperature is favourable to animal and vegetr 

 able life. — Caufe of the increafed violence of the wefterly winds, deduced from the forefts of 

 Ireland inparticular, and of Europe in general, having been cleared in modern times, and the 

 land cultivated, 



III. Experiments and Obfervations on Eleftricity — Excitation — The two 

 States — Points of Difference between the Aftion of weak and ftrong Elec- 

 tricities compared together. (W. N.) — — P- 43^ 



Cafcade of eleftric fire produced by cutting a hole in the filk flap of the rubber. Beautiful ftar formed 

 by the plus electricity upon paper. Experiments to determine whether the glafs tube in Ben- 

 net's eleftrometer has any efFeft on the divergence of the gold leaf. Other enquiries refpefting 

 the metallic coatings and lize of the head of that inftrument. — Whether the electricity of con- 

 dudors is difturbed according to the fame law, by the influence of an ele(ftrified body, when the 

 power is weak, as when it is ftrong. Remarkable diff^erence in the operation of pointed bodies 

 and. flame in weak and Itrong eleftricities. — Whether the laws of attraftion and repulfion be the 

 fame in ftrong eledricity as iu weak. 



iV. Analyfis of the Red Lead of Siberia ; with Experiments on the new Metal 

 it contains. By Citizen Vauquelin, Infpeftor of Mines, and Confervator 

 of Chemical Frodufts at the Mineralogical School. (Concluded from page 

 393, Vol. II.) _____ p. 4^,1 



Combinations of the acid of led lead with the alkalis. — Its reduftion to the metallic ftate. — Proper- 

 ties of the new metal. — Denomination and ufes in chemiftry and the arts. 



V. Experiments to determine the Denfity of the Earth. By Henry Caven- 

 diHi, Efq. F.R.S. and A.S. ~ _ — p. 446 



A wooden arin fix feet long was fufpended in a horizontal pofition by a flender wire forty inches 

 long, and to each extremity was hung a leaden ball about two inches in diameter. To thefe 



d a balls 



