CONTENTS. 



u Principles of the Science of Tuning Instruments with 

 fixed Tones." . . . . 292 



Memoir upon the Formation of the Phosphoric Ether, by 

 Means of a particular Apparatus. By M. Boullay, 

 Chemist, in Paris 302 



Memoirs of the late Erasmus Darwin, M. D. . . 305 



Observations upon Subterraneous Heat, made in the Mines of 

 Poullaouen, and of Hnelgoat, in Br it any, in France 320 



Method of ascertaining the Value of Growing Timber Trees, 

 at different and distant P&riods of Time . . 327, 350 



Report on the ponderous Flint Glass intended for the Ma- 

 nufacture of Achromatic Glasses. Ptesented to the Insti- 

 tute by M. Doufourgkrais • 337 



Description of an improved Telegraph 343 



Description of an Improvement in Jury Masts . . , . 346 



Improvement in Anchors, to render them more durable and 

 safe for Ships ; and an improved Mode of Fishing Anchors 



348 



On the intended Thames Archway between Rot her hit he arid 

 Lirilehouse 372 



On the Fibres used in Micrometers: With an Account of a 

 Method of removing the Error arising from the Inflection 

 of Light, by employing Hollow Fibres of Glass . . 383 



Observations suggested by the Geological Paper of Mr. 

 John Farey 385 



Introduction to the Study of Mineralogy. By M. Hauy 



38y, 45(> 



A new Method for detecting Arsenic 401 



On the present Mode tf finding the Rates of Timekeepers 402 



Thoughts on Atmospheric Density and Pressure . . 417 



On Geometrical Proptfi'tion 426 



A few Hints concerning the Benefit that may be expected 

 from the Nature of Coal Gas 432 



On the fertilizing Properties of Manures which contain 

 Ammonia .. .. .. ? . .. 43 S 



Geological Observations on the Excavation of Valleys^ and 

 local Denudations of the Strata of the Earth in particular 

 Districts, &c, in Reply to Mr. Jqhn Carr's Letter 

 in the last Number, p. 385 442 



Contrivance for preventing Doors from Dragging on Carpets 



448 



Description of an Improved Screw Wrench to fit different- 

 sized Nuts or Heads of Screws 450 



On the Natural Causes which operate in the Formation of 

 Valleys 452 



Reply to Mr. Barlow's Article on Floating Bodies . . 4] 6 



