Description of an Improved Long Slide- Valve, <$•<?. 3G1 



Genus 5. — Coelodon, Lund. 



Dentes j~ 

 Genus 6.— Sphenodon, Lund.* 



Description of an Improved Long Slide- Valve for Condensing 

 Engines, By Mr John Maxton, F.R.S.S.A., Engineer, 

 Leith. Communicated by the Royal Scottish Society of 

 Arts. With a Plate.t 



The advantages of this valve are, — that it may be used 



without a steam-chest, while it has all the advantages of a 

 long slide-valve in shortening the passages to the cylinder, it 

 works with much less friction than the common long slide- 

 valve, the pressure being equalized, and is much less expen- 

 sive, and easier upheld, than the packed valve. 



In fig. 1, Plate VII., the piston is represented as de- 

 scending in the cylinder, the vacuum being formed under 

 the piston by the passage A through the valve towards the 

 condenser, the steam being admitted above the piston by 

 the induction passage B, the steam at the same time having 

 access to the portion of the valve below at D, which tends to 

 press the valve outwards from the cylinder, while the vacuum, 

 acting on the inside of the valve E, draws it towards the cy- 

 linder, the valve being so proportioned that the vacuum must 

 so far overbalance the steam, that the valve will keep close 

 to the cylinder. 



* Both this genus £ind Ccelodon, Lund, are indicated rather than satisfactorily 

 established. The teeth of the Sloth are first developed in the form of hollow 

 obtuse cones, and do not assume the cylindrical form until worn down to the 

 part which has acquired, in the progress of growth, the normal thickness ; and 

 this is afterwards maintained, without appreciable alteration, during the subse- 

 quent uninterrupted growth of the tooth. The compressed molars of the Scelido- 

 therium, which doubtless follow the same law of derelopment, would present in 

 the young animal the form of hollow wedges ; and such I suspect to be the na- 

 ture of those teeth, which are figured by Dr Lund in the above-cited Danish 

 Memoir, plate xvii. figs. 5-10, and on which he has founded his genus Sphenodon,* 



t Read before the Royal Scottish Society of Arts, 13th March 1843. 



Owen on the Mylodon ro^wtns, p. 168. 



