xxxiv 



architect ; but as, through age and infirmity, he was unable to proceed with 

 it, the whole plan was remodelled and rendered practicable, and the arch 

 equilibrated with great scientific precision by Mr. Rennie, who further 

 showed his constructive power by devising a very ingenious centre for sup- 

 porting the arch during the process of building. 



Mr. Rennie took much interest in the question of propelling vessels by 

 the screw. The screw-propeller had been already tried at various periods 

 and in various forms. Mr. Rennie' s attention was specially drawn to the 

 subject in 1836, by certain successful trials then made by Mr. Pettit Smith 

 with a screw-propeller fitted to a sm.all open boat. After due considera- 

 tion of the results of this experiment, Mr. Rennie was satisfied that the 

 method would be practicable and advantageous when applied on a larger 

 scale, insomuch that he and his brother, at no small pecuniary risk, com- 

 bined with some other enterprising persons to carry it into effect, and a 

 vessel called the 'Archimedes ' was built for the purpose, and fitted with a 

 screw driven by engines of 80 horse-power. Notwithstanding adverse pre- 

 dictions, the 'Archimedes' succeeded perfectly ; and the Messrs. Rennie 

 subsequently, in 1S40, constructed for the Admiralty an iron vessel of 210 

 tons and fitted it with a screw-propeller, by which a speed was obtained of 

 twelve and a quarter miles per hour, which was four miles above the rate 

 of the Admiralty paddle-steamers of that period. This vessel, the ' Mer- 

 maid,' was the first screw-propelled ship in the British Navy, and her intro- 

 duction is a memorable event in the history of steam navigation. 



Throughout his busy practical life Mr. Rennie bestowed much time and 

 thought on the scientific side of his profession, and undertook various ex- 

 perimental inquiries on physical questions connected with it. Three papers 

 containing the results of some of his investigations are published in the 

 Philosophical Transactions, viz. ''On the Strength of Materials," in 1818 ; 

 " On the Friction and Abrasion of the Surfaces of Solids," in 1829 ; and 

 "On the Friction of Fluids," in 1831. ' To the British Association for the 

 Advancement of Science he made two communications on the Quantity of 

 Heat developed by Water when rapidly agitated, and presented to the same 

 body an elaborate Report on the progress of Hydraulics as a branch of En- 

 gineering, published in the volumes for 1833 and 1834; also Reports on 

 Railway Constants (1838), and on the Changes in the Channels of the 

 Mersey (1855 and 1856). He is the author of various contributions 

 on bridges, water-wheels, and other subjects of practical engineering, in the 

 ' Transactions of the Institution of Civil Engineers,' in ' Weale's Papers,' 

 and in Woolhouse's edition of ' Tredgold on the Steam-engine.' He also 

 brought out a new edition of ' Buchanan on Machinery,' and added much 

 new matter. 



Mr. Rennie was elected a Fellov/ of the Royal Society in 1822 ; in 1845 

 he was nominated a Vice-President, and appointed Treasurer in succession 

 to the late Sir J. W. Lubbock^ which office he held till 1850. He was also 

 a member of several foreign academies. 



