38 Mr Hen wood's account of the 



sent, with several engineers and scientific men. Following Mr 

 Grose's idea, Mr Woolf has brought one of his engines to an 

 average duty of nearly seventy millions, and other engineers 

 still following are not far behind. Its effect will be traced 

 by inspecting the tabular view which accompanies this article. 

 Ignorance of this important object precludes, in many in- 

 stances, xhafnll benefit being now derived from its application ; 

 but its partial adoption must in every case be beneficial. 



Mr Grose has realized a similar advantage in other engines, 

 and it would have afforded us'great pleasure to have given a 

 view of other important improvements which he contemplates ; 

 but as they are not yet in operation, it would now be prema- 

 ture ; however, we hope soon to be able to lay a detail of them 

 before the public, in an early number of the Edinburgh Jour- 

 nal of Science. 



On some peculiarities in the construction and manner of work- 

 ing usual in CornzvalL 



It is found in practice that the maximum effect from a 

 given quantity of fuel, obtains when the fire is from eighteen 

 to twenty-two inches below the highest part of the concavity 

 of the inner tube ; when the depth of ignited matter does not 

 exceed fourteen inches, and is not less than eight ; and when 

 the boilers are sufficiently capacious to supply the requisite 

 quantity of steam, the damper being so far closed as to allow 

 the whole of the smoke to pass slowly to the chimney, but still 

 so rapidly as to keep a bright fire without any other stirring 

 than the removal of the cinders requires. If the draught be 

 too slow, the brightness of the fire will diminish, and the smoke 

 and heated air will escape at the fire doors, which must be at- 

 tended by much loss of caloric, as well as by great inconveni- 

 ence to the attendant. If the draught be too brisk, the gaseous 

 matter will pass so rapidly through the fuel as to escape to 

 the chimney before its temperature has been reduced to that of 

 the boiler. 



The same effect will obtain, if a fire deeper than fourteen 

 inches be made, and the damper opened so far as to keep up a 

 brisk flame ; and if the fire be less than eight inches deep, it 

 will permit the influx of a disadvantageously large quantity of 



