vlii CONTENTS. 



The inftruincnt confifls of two radii conneifled together at the angle, by a fpring, in the fame manner 

 as dividers and oiher well-known implements. The explofion from a fmall cannon drives thefe 

 legsafunder, and the quantity of their divergence ismeauired by a. graduated arc and Aiding piece. 



IV., ,An Account of fome Endeavours to alcertain a Standard of Weight and 

 Meafure. By Sir George Shuckburgh Evelyn, Bart, F.R.S. and A.S. (Con- 

 tinued from page 146) - - - " P* ^oo 



Accurate determination of the lengths of the exifting ftandards of longitudinal meafure, kept at the 

 apartments of the Royal Society, in the Tower of Londo") and in the Exchequer. Comparifon of the 

 weights ufed by the author, with the Troy pound conftrufted by order of the houfe of commons 

 by Mr. Harris, in 175B, General remarks, with fonie obfervotions on the prices of provifions at 

 different periods of our hiftory. 



V. Defcription of a new Arrangement pf the Bars ja - the Gridiron Pendulurn, 



with a Drawinsr. (W. N.) ' ' "- V - ' •;--,-; '', -' p. 20c> 



, ,^ ( .([ -'=' ^ , . ■'/:f:J iC ?:>'.- \.. . ' 



The^ovelty of this pendulum confifts in the arrangement of the ftecl bars r,o^ ^^o.^ of jZini9^j^Bd 

 in a fimple iiiiethod of adjulling the lengtiis required for the compenfation, '„■,. ..;,'y . ■* [. • • 



VI .On the Epocha of the Difcovery of the Tclefcope, and the Opinion of 



Boyle that. Plants derive their Nourifhment from. Water only, By Cit. 



Boiffonade ' • ' - - '^ ' *' . ' \ ■'? ''•'■- ' p. 207 



.-3 ;.,.'l ■ ' .. 



Account of an ancient drawing, defcribed by Mabillon, and" alfo of a paflage in Strabo, which have been 

 thought to render it probable that the ancients were acquainted with the telefcope. Reafons why 

 thefe documents ought not to be confuiered as conclufive. Whether fpeflacles were known in the 

 thirteenth century. Quotation in proof that the nourifhment of plants, chiefly by water, was known 

 much earlier than the time of VanhelmODt^ andnBoyle. 



VII. Obfcrvations on' the Proportion o-f real Acid in the three known naineral 

 Abids, and on the Ingredients in various neutral Salts and other Compounds. 

 By Richard Kirwan, Efq. LL.&r^.-R.S. and M.R.I. A. - p. 2 10 



Introdu<flory remarks. Experiments on the changes of denfity in acids by heat. Tables of the quan- 

 tities of real acid contained in vitriolic, nitrous, and marine acids of different denfities; of the quan- 

 tities of acid taken by the feveral alkalies and earths; of the quantities of alkalies and earths 

 taken up by the feveral acids ; of the quantities of neutral fait afforded by 100 parts of each of the 

 feveral alkalies, earths, and acids ; and alfo of the proportions of ingredients in thefe falls. 



VIII. On a fubmarine Foreft on the eaft Coaft of England. By Jofeph Correa 

 ' de Serra, LL.D. F.R.S, ^nd A.S. - - - p. 216 



Account of certain iflets on the coaft of Lincolnlhire, which are chiefly compofed of decayed trees. 

 The fame ftratum of vegetable remains extend beneath large trafts of the neighbouring country. 

 Interefting enquiry concerning the former ftate of this fubmarine foreft, and the caufes of its pre- 

 • fent ftate. 



IX. Optical Remarks, chiefly relating to the Reflexibility of the Rays of Light. 

 By P. Prevofl, Profeffor of Philofophy at Geneva; of the Academy of Berlin ; 

 of the Society d<.s Ciirieux de la Nature ; and of the Royal Society of Edin- 



. burgh - - - " " P- 2*2 



Enquiry 



