so Biographical Memoratida 



(HI the subject. " But although our conduclors are inadequate 

 to so great a power as that wliicli is necessary to exhaust cloud« 

 of an iimnense size, yet they may be appHed with great proba- 

 bihtv of success to carry off with safety as much lightning as 

 may at anv given time be contained in the tnet;r]lic parts of a 

 t)uilding, provided a complete communication be formed be- 

 tween them and sufficiently large conductors." 



Impressed with a high opinion of Sir Isaac Newton's disco- 

 veries in optics, and bv a close attention to those experiments 

 which Sir Isaac Newton made, and has detailed in his Book of 

 Optics. Mr. Delaval showed by a series of ex|)eriments, and 

 minute observations that iSir Isaac Newton's doctrine is equally 

 applicable to permanently coloured bodies ; and on January 24,> 

 176.5, a Letter addressed by Mr. Delaval to the Earl of Morton, 

 President of the Royal Society, was read there, containing Ex- 

 periments and Observations on the Agreement between the 

 specific Gravities of the several metals, and their Colours when 

 united to Glass, as well as those of their other Preparations. 

 This paper is published in the fifty-fifth volume of the Royal 

 Society's Transactions, and for it Mr. Delaval was honoured with 

 their gold medal. 



In 177'5, Mr. Delaval and Mr. B. Wilson were engaged in a 

 Series of Experiments relative to phos])horic and the prismatic 

 Colours they are found to exhibit in the Dark. The account 

 was published by Mr. Wilson, who stated that the experiments 

 were made in Mr. Delaval's house on the side of the Thames at 

 Westminster. 



In 1777, Mr. Delaval published in quarto. An experimental 

 Inquiry into the Cause of the Changes in opaque and coloured 

 Bodies, with an historical Preface relative to the parts of philo- 

 sophy therein examined, and to the several arts and manufactures 

 dependant on them. 



On the 1 9th of May 1784, Mr. Delaval jiroduced his experi- 

 mental Inquiry into the Cause of the permanent Colours of 

 o])a(|ue Bodies, which was ])resented and read at the Literary and 

 Philosophical Society of Manchester, and honoured with their 

 gold medal. It is published in the second volume of the second 

 edition of their Memoirs. 



In testimony of the great merit of Mr. Delaval's discoveries 

 and observations, I adduce the approbation they have generally 

 experienced amongst men of science, and which is evidenced by 

 their having been translated into most of the European lan- 

 guages. 1 beg leave to quote the following instance, transcribed 

 from the Nouvmux Memoires de V Jcademic Royal des Sciences 

 et Belles Lellres, noted by M. Le Professeur de Castellon, re- 

 specting 



