TBANSACTIONS OF SECTION G. 877 



2. As to sclietne being too complicated. 



It is quite true that any scheme of mechanical ventilation is more complicated 

 than schemes of natural or so-called automatic ventilation; but Plenum schemes 

 are by no means too complicated for successful working, as is proved by the 

 experience gained in all parts of the globe. 



To say that a natural scheme of ventilation is uninterruptedly at work all the 

 year romid is, to say the least, very misleading. It may be true that the atmo- 

 sphere is always in motion ; but then this motion may be so infiuitesimally small at 

 times as to cause no movement of air at all in our buildings — a state of affairs 

 well known to all those who have to rely on this kind of ventilation. r 



The addition of the machinery is a safeguard for the regular supply of air in 

 the proper quantities, and it is far better and wiser in all matters concerning so 

 immediately the health of countless thousands as ventilation does to have a special 

 man constantly attending to it, rather than leave it to itself, and all sorts of 

 mishaps. 



3. As to cost of scheme. 



It is undoubtedly a most important matter to consider very carefully the cost 

 of any ventilation scheme ; but when comparing the expenses in connection with 

 two different modes of ventilation for one building, great care must be taken to 

 place the two schemes exactly, as far as this is possible, on the same basis as to the 

 purity of air supplied, the quantity, the regularity, the convenience of working 

 them, &c. If this is not done the results obtained will be utterly useless and mis- 

 leading ; but whenever this is done, and all the circumstances of the case considered, 

 the author is confident that the expenses in connection with the Plenum system 

 wiU not be found excessive. He has not prepared any figures, as he is of opinion 

 general figures are frequently totally misleading, and for this reason he would 

 recommend the consideration of the question of cost afresh for each particular case. 



Concerning the value of other methods of ventilation, one of which it may be 

 necessary to adopt where the Plenum system cannot be installed, the author wishes 

 it to be understood that he by no means' condemns them; that, on the contrarv, 

 each has its special advantages under certain conditions. In each individual case 

 the ventilating engineer will have to investigate first its special circumstances and 

 requirements, no two cases being alike, and then he will have to select his scheme 

 accordingly. 



In concluding his remarks on warming and ventilation the author desires to 

 make it clear that his aim throughout has been to state his case fairly and fully, 

 and he trusts he has succeeded in this ; if, at the same time, he has been able to 

 increase the interest in this question of vital importance, then all his efforts will be 

 well repaid. 



6. On Modern Watchmaking. By T. P. Hewitt. 



7. On Patent Percussive Tool for Calking, Chipping, Mining. 

 By J. MacEwan Ross. 



The tool which the author now brings under notice is composed of few parts, 

 and those are of the most substantial character. 



The piston is a solid steel forging, truly turned and ground into the cylinder, so 

 as to work or float quite freely, and this is the only moving part in the tool. It is 

 about 3 in. long, slightly reduced at the centre where the actuating fluid is intro- 

 duced into the cylinder. 



The handle of the outer casing is cast hollow. One side is truly bored out and 

 fitted with a brass piston valve covering the outlet of exhaust. 



This valve is fitted with a trigger which when drawn back by the finger sets 

 the tool in motion by allowing the exhaust to escape. 



One man, by the use of this tool, can do as much work in a given time as five 

 to ten men can do when calking by hand. 



The principle upon which the tool works is as follows. The piston is turned 



