TO CORRESPONDENTS. 



Our thanks are due to Dr. T. Forster for the Register of Thermometrical 

 Observations at Sm\Tna. 



Since Mr. P. Newton's paper on the Triscction of a Circular A.c wa« 

 printed, that Gentleman has informed us that he has succeeded in removing 

 or avoiding the hj-pothetical point respecting the Lune, and that we may 

 expect a continuation of his remarks. 



PRACT^CAI- MECHANICS. 



This day is published, handsomely printed in two vols, octavo, illustrated 



with 20 plate? and numerous figures, Price ll. 6s. in Boards, 



PRACTICAL ESSAYS on MILLWORK and other MACHINERY; 

 viz. on the Teeth of Wheels ; the Shafts, Gudgeons, and Journals 

 of Machines ; the Couplings and Bearings of Shafts ; disengaging and 

 re-engaging Machinery in Motion; Equalizing the motion of Mills; 

 changing the velocity of Machines in motion, and the framing of MilJ 

 work ; with several useful Tables. 



By ROBERTSON BUCHANAN, Engineer. 



The Second Edition revised, with notes and additional articles containing 

 new researches on various Mechanical Subjects : 



By THOMAS TREDGOLD, Civil Engineer, &c. 



Printed for J. Taylor at the Architectural Library, No. 52, High 

 Holborn. 



Also handsomely printed in octavo, illustrated with two large plates. 

 Price 4s. sewed, 



DESCRIPTION of a RAILWAY" on a new Prl.iciple ; with observa- 

 tions on those hitherto constructed, and a Table showing the comparative 

 amount of resistance on several now in use: also an illustrr.tion of a newly 

 observed fact relating to the friction of Axles, and a description of an im- 

 proved Dynamometer for ascertaining the resistance of floating vessels and 

 carriages moving or Roads and Railways. 



By H. R. PALMER, Civil Engineer. 

 Where d?o may be had 

 SMEATON'S REPORTS, 4 vuls. quarto, 51. 10s. Boards. 



N. B. All works on Architecture, theoretical and practical, also Civil 

 Engineering, are constantly on sale at Taylor's Architectural Library, 

 with a liberal discount for ready money. 



ENGRAVINGS. 



Vol. LIV. A Plate Illustrative of the Menai Bridge.— A Plate illus- 

 irativs of Mr. Lowe's Dt.scription of a Mercurial Pendulum. — A Plate 

 illustrative of Mr. Hare's Calorimotor, a new Galvanic Instrument. — A 

 Plate illustrative of Captain Sabine's Paper on Irregularities observed in 

 the Direction of the Compass Needles of the Isabella and Alexander in 

 tl-e late Voyage of Discovery ; and Mr. Scoresby's Anomaly in tlie Va- 

 r'uiion of th« Magnetic Needle as observed on Ship-board. 



Vol. LV. A Plate exhibiting Sketch of the Comet's Path of July 1819. 

 — A Plate illustrative of the Annular Eclipse of the Sun on the 7th of 

 St'Jtcrnber next. — A Plate illustrative of Mr. Lane's Instrument for 

 '.;u;.".cring Eiuitj Mr. Youkg's Mode of preparing Opium from the 



