512 MEMOIR OF DANIEL TEEADWELL. 



cent more wood and thirteen per cent more water when the sparker is on than when it is off. As tlie 

 draft of air through the Are and ehimnej' is less rapid when the sparker is upon the engine, we should 

 expect to find the combustion less perfect, and consequentlj- a greater quantitj- of wood required to pro- 

 duce a given effect, measured either Iw the evaporation or the power of the engine. We should not onh' 

 expect a diminished effect from these causes, but likewise, as the time in passing over the road was 

 greater when the sparker was upon the engine, there must have been a greater loss of heat from the ra- 

 diating and conducting surfaces exposed to the atmosphere. The experimeuts, therefore, in this case 

 accord with the conclusion which we should form a jyriori. This, however, does not apply to the 

 water, and we should expect to find that in this, as in other cases, the power would bear a close relation 

 with the water expended. It will be observed, however, that there is a departure from this relation 

 in the water used in all the experiments compared with the power as measured bj- the dynamometer, as 

 the engine went up or down the road, and that from ten to fortj'-five per cent more water was used in 

 proportion to the draft in the descending than in the ascending journeys. I cannot believe that anj- mis- 

 take was made in the measure of the water, and I know of no circumstance to which to attribute the 

 ditterence but the greater velocitv of the pistons in descending than in ascending the road, and to the 

 steam being worked at a much less elastic force. These would both diminish the power from a given 

 quantity of water formed into steam, perhaps in a degree sufficient to account for the apparent dis- 

 crepancy. Neither of these circumstances is to be found, however, when we compare the passages, both 

 up and down the road, with the sparker, against the same passages made without the sparker, and j'et we 

 have found that more water was required under the former than under the latter condition. The quan- 

 tity of water, however, is of no importance in itself, and I have only stated it here for the purpose of 

 bringing everything observed in the experiments into notice. I sliall leave it with stating that the en- 

 gineers who manage the engines on the Worcester road have an opinion that the resistance produced b}' 

 the sparker to the free passage of the steam from the chimne3- after it has jiroduced the stroke adds in 

 some degree to the load of the atmosphere against which the piston is moved. This resistance must 

 necessarily be very small, and it may well be doubted whether it be sufficient to be appreciated. 



In comparing the velocities with and without the sparker, we find, if we add the nine per cent as in 

 the former comparisons, that the time required for equal effects was about twentj-three per cent more 

 when the sparker was on than when the engine was used without it. 



The conclusion then is irresistible, that, under everj- relation of speed and economy, the sparker is in 

 some degree disadvantageous. At the same time, it cannot be doubted that the comfort of the passen- 

 gers, and to some extent their security and that of their property-, are increased by it.* 



II. Next for the effect produced h\j engines of diff'erent sizes. — We find that in transporting one 

 ton of 2,240 lbs. to and from Framingham, which maj- be taken as equivaleut to a level railroad of 41 

 miles in extent, the consumption of wood and water was as follows, f 



From this it appears that, contrary to the common opinion, the greatest effect was produced from a 

 given quantity of fuel when used in the smallest engine. I entertain no doubt, however, that this was 

 from the better condition and adjustment of that engine, which, tliough not apparent to common obser- 

 vation, for all the engines appeared in equally good order, yet really existed, and that the largest engines 

 when equal in construction and in equal order will produce somewhat greater effects than the smaller. 

 Moreover, the expense for the engineer and otlier persons required for the management of the engine 



* Some form of sparker is used at the present time, on all locomotives. — W. 



t I take only the trials where the -sparker was not used, as the locomotive engine is at present most commonly used in 

 that form. 



