RAMSDEN. 



pointed out ,i new method and apparatus adapted to the 

 conveyance and fupport of the portable barometer. Mr. 

 Ramfden made improvements on the cleftrical machine ; and 

 on manometers for meafurinsf the dcnfity of the air : he in- 

 vented an inllrument for meafuring inacceflible diftances : 

 aiTaying balances which turn with lefs than a ten thoufaudth 

 part of the weight ufed : levels and a variety of other in- 

 ilruments. Tlie pyrometer alfo exercifcd ins talents, and 

 on this occafiop, as on all others, Mr. Ramfden fhewed a 

 fort of natural and almoll intuitive fagacity in difcovering 

 the eflential faults of an inltrumcnt, and in inventing the 

 moil fimple and exadl methods of correfting them. With 

 refpeA to optics, he difcovered a method of correfting, in 

 a new and perfect manner, the aberration of fphericity and 

 refrangibility in compound eye-glnlies applied to all aliro- 

 nomicaliiiftruments. Opticians had imagined that thepurpofc 

 might be accomplifhed by making the image of the objeil- 

 glafs fall between the two eyc-glairt:s, which was attended 

 with this great inconvenience, that the eye-glafs could not 

 be touched without deranging tlie line of collimation, and 

 the value of the parts of the micrometer. To remedy this 

 inconvenience, he fet out from a fimple experiment, viz- that 

 the edges of an image obferved through a prifm are lefs 

 coloured, according as the image is nearer the prifm. This 

 led him to attempt placing the two cj^e-glafles between the 

 image of the objeil-glafs and the eye, without failing to 

 correA the two aberrations ; which he did by changing the 

 radii of the curves, and placing the glafTes in a manner very 

 different from that commonly employed. In the Philofo- 

 phical Tranfadlions for the year 1779, Mr. Ramfden has 

 defcribed a new reflefting objeft-glafs micrometer ; to the 

 paper on this fnbjecl we refer our readers, and alio to the 

 article Micrometer in this Diftionary. With this micro- 

 meter the diameters of the planets may be meafured ; it 

 may be adapted to all kinds of achromatic telefcopes ; it 

 may be brought near to, or removed from, the objeft-glafs 

 at pleafure, to render viilon diftinft ; and it may be removed 

 from the telefcope, if the obferver wifh to uie the latter 

 without a micrometer. The high degree of merit to which 

 Mr. Ramfden's many and important inventions were intitled, 

 led his friends to propole him as a member of the Royal 

 Society, and he was eletted in the year 1786. 



The Equatorinl or Tranfu inftrument (fee the articles) re- 

 ceived great miprovements in the hands of Mr. Ramfden, 

 who rejected the endlefs fcrew, which by preffmg on the 

 centre deilroyed its precilion ; he placed the centre of gra- 

 vity on the centre of the bafe, and caufed all the movements 

 to take place in every dirottion ; he pointed out the means 

 of reftifying the inftrument in all its parts, and he applied 

 to it a very ingenious fmall machine, for meafuring or cor- 

 recting the cffed\ af refraction. The greatelt equatorial in- 

 ftrument ever attempted, is that which he conftruCted for llr 

 George Shuckburg, on which he employed feveral years, 

 and of which vve have given a defcription and figure. Mr. 

 Ramfden's meridian telefcopes which he made for Blenheim, 

 Manheim, Dublin, Paris, and Gotha, are alfo remarkable 

 for the excellence of tlieir objeft-glaffes. With that of 

 Dublin, Mr. Ufher obferved ftars of the fourth magnitude 

 in the open day, and thofe of the third very near their con- 

 junftion with the fun. Thcfe telefcopes are eight feet in 

 length. There is a live- feet one at the obfcrvatory at Pa- 

 lermo. Mr. Ramfden made great improvements in the mural 

 quadrant, of which a full account will be found in the article 

 Circle, to which we refer our readers for much valuable 

 information on tlie fubjeft of ailronomical inftruments. Hav- 

 ing in various parts of our work entered into the nature 



of Mr. Ramfden's improvements and inventions, it ie unue- 

 celTary to repeat here wh»t has already been fully explained. 



The field in which the inventive genius and fuperior talents 

 of Mr. Ramfden were cxercifed, was, as we have feen, very 

 extenfive. In order that every part of his inftruments might 

 be fabricated under his own inlpeftion, he collefted in his 

 workfhops men of every branch of trade necclfary for their 

 conltruftion. So important did he coufider the principle of 

 divifion of labour, that he always confined the fame workmen 

 to the iame branch, and by that means arrived at the greatell 

 correcinefs and nicety in executing it. Notwithdandin"- the 

 great perfection of his inftruments, which ought :o have fe- 

 cured to Mr. Ramfden a large fortune, he fold them cheaper 

 than any other artift in Lond m, fometimes even one-third 

 below the ufual price. Such was the demand for them, 

 from almoft all parts of the world, that though he employed 

 fixty men, he was unable to execute all the orders which he 

 received. His great attention tobufinefs injured his health, 

 and haftcned his death. Ho died at Brighton, where he 

 had been for the benefit of the fea-air, November 5, 1800, 

 in the fixty-fixth year of his age. He had been elefted a 

 meniber of the Imperial Academy of Sciences at Peterlburg 

 in 1 794, and in the following year he was prefented with the 

 gold medal, adjudged by the Royal Society to perfons dif- 

 tinguifhed for their fcientific talents. 



Mr. Ramfden was by nature endowed with uncommonly 

 ftrong reafoning powers, and a moft accurate and retentive 

 memory, but, at the fame time, with fuch a quicknefs of 

 penetration, that he could, as it were, with a fingle glance, 

 view in every light the fubjeCi on which he thought, and 

 adopt the moft advantageous mode of confidering it. He 

 poflefTed, in an cxquifite degree, that quality of mind 

 which is emphatically ftyled elegance, which in the abltraft 

 fciences leads to clearnefs, fimplicity, and precifion, as in the 

 fine arts and literature, it gives the laft polilli to genius, and 

 is more generally known by the appellation of tafte. In his 

 habits he was temperate to abltemioufnels, fatisfied with 

 fmall quantities of food, and a fmall portion of deep. Un- 

 acquainted with difiipation or amufement, and giving but 

 little time even to the fociety of his friends, the whole of 

 thofe liours which he could fpare from the duties of his pro- 

 feflion, he devoted cither to further improvements in his in- 

 ftruments, or to the perufal of books of fcience, particularly 

 thofe mathematical works of the fubUme writers which had 

 any conneftion with the fubjeft of his own purfuits. Mr. 

 Ramfden's only relaxation from almoft conllant and fevere 

 itudies, was the occafional perufal of the beft authors, 

 both ia profe and verfe ; and when it is recollected that at 

 an advanced age he made himfelf fo coinpletely mafter of 

 the French language, as to read with peculiar pleafure the 

 works of Boileau and Moliere, no one can believe that he 

 mis-fpcnt even his hours of amufement. Short and temperate 

 as were his repafts, a book or a pen was the conftant com- 

 panion of his meals ; and when illnefs broke his fleep, a 

 lamp and a book were ever in readinefs to beguile the fenfe 

 of pain, and make bodily ficknefs minifter to the progrefs 

 of his mind. He was well ikiUed in the abftruler parts of 

 mathematics, and converfant with the belt writers on the 

 fciences ; and fuch was his manual dexterity, that there was 

 not one tool in any of the numerous branches of his profel- 

 fion which he could not ufe with a degree of perfection 

 equal to that of the very beft workman in that particular 

 branch, and he could have begun and finiftied every fingle 

 part of his moft comphcated inftruments. For this article 

 we are chiefly indebted to a very elaborate and excellent ori- 

 ginal memoir in the 8th vol. of the Gen. Biog. 

 ^ RAMS- 



