440 PHILOSOPHICAL TRANSACTrONS. [aNNO I767. 



of light on the whole subject. The lengths of the times then between the 

 changes of brightness, if he is not mistaken, depend on the duration of the per- 

 ception before mentioned, occasioned by the impression of the light upon the eye, 

 than which they seem to be neither much longer nor shorter. Whatever inequa- 

 lities fall within a much shorter time than the continuance of this perception, will 

 necessarily be blended together, and have no effect, but as they compose a part 

 of the whole mass ; but those inequalities which fall in such a manner as that 

 they may be assigned to intervals nearly equal to, or something greater than the 

 continuance of this perception, will be so divided by the imagination, which will 

 naturally follow, and pick them out as they arise. 



XXF^lIl. Thermometrical Observations at Derby, By Mr. John fVhitehurst,* 



p. 265. 



We experienced a much greater degree of cold at Derby, in the late frost, than 



* Mr. Whitehurst was born April 10, 1713, at Congleton, in Cheshire, where he inherited a 

 small estate possessed by his ancestors from the conquest ; and he died at London, the 18th of Feb- 

 1788 ; nearly at 75 years of age. Though his education was confined, and he was brought up to his 

 father's business of clock and watch-making, in this, as well as in other mechanical and scientific 

 pursuits, he soon gave indications of future eminence. On quitting his father, he set up for him- 

 self in the same line at Derby, where he made the town-clock at the town-hall, and the clock and 

 chimes in the tower of AU-saints-church in that town. While resident there, besides his constant 

 attention to his own professional business, he was consulted as an engineer in most of the under- 

 takings in the neighbouring country, where the aid of superior skill, in mechanics, pneumatics, and 

 hydraulics, was requisite. Being appointed stamper of the legal money-weights, when the act 

 passed in 1775, for regulating the gold coin, he removed to London ; where, to the time of his 

 death, his house became the common resort of the scientific and ingenious of all ranks and nations. 

 In 1778, Mr. W. published the first edition of his " Inquiry into the Original State and Formation 

 of the Earth j" an ingenious work, originating from his various scientific researches made in Derby- 

 shire, while he resided in that county- He was elected a f. u. s. in 1779 ; of which he proved a 

 very useful member, and he communicated some ingenious papers to the Phil. Trans. In 1787, he 

 published " An Attempt towards obtaining Invariable Measures of Length, Capacity, and Weight, 

 from the Mensuration of Time." This is founded on a standard of length, assumed from the mea- 

 sured difference in length, nearly 60 inches, between two pendulums, of which the one was 84 

 inches in length and vibrated 42 times in a minute, the other of 20 inches vibrating 84. times in a 

 minute. Afterwards, till the time of his death, Mr. W. very much occupied himself in composing 

 a treatise on Chimneys, Ventilation, and the construction of Garden-stoves ; a work which was, 

 after his death, published by his friend Dr. Willan. In short, Mr. Whitehurst was indefatigable in 

 his researches after knowledge, in his endeavours to communicate it to others, or in devising and 

 constnicting useful machinery. But how resiiectable soever he was in mechanics, and those other 

 parts of natural science which he more immediately cultivated, he was of still far higher account 

 with his acquaintance and friends on th;e score of his moral qualities, being like the true Israelite in- 

 deed in whom there was no guile. 



See a much fuller account of Mr. W.'s life, given by Dr. Hutton as an introduction to the edition 

 of his works printed by him, with notes, in 1792. 



