TRANSACTIONS OP THE SECTIONS. 103 



horse-power, which was stated to be now generally computed by all makers 

 and purchasers of steam-engines from the diameter of the cylinder and length of 

 the stroke, taking in round numbers each such nominal horse-power as capable of 

 raising 60,000 lbs. one foot high with a given consumption of fuel : Watts's old 

 rule of 33,000 lbs. had long been abandoned, the principle on which it was origi- 

 nally founded being now understood as incorrect, though after all it was but a con- 

 ventional expression. The Commissioners who had been appointed by the Board 

 of Trade to investigate into and report upon the atmospheric railway, had not even 

 used Watts's rule correctly, and by this, and by reasoning and calculating on the 

 exhausting-pump employed in their experiments as theoretically perfect, and by an- 

 other unintentional misapprehension, the horse-power stated in their report as ne- 

 cessary to work tubes of certain lengths and diameters, was put nearly double the 

 horse-power as understood by the practical engineer. Some of the other opinions 

 and conclusions of the Commissioners were also adverted to and their soundness 

 impugned. 



It was then pointed out, that by means of self-regulating valves of a very simple 

 character, drawings and models of which were exhibited, the trains might pass on 

 continuously without necessarily stopping B.K each stationary engine ; and it was 

 also particularly observed, that it did not appear to be either necessary or advisable 

 to vary the diameter of the tubes at each variation of gradient ; but that the most 

 convenient arrangement would be to have the tube or main by no means limited in 

 diameter, and to work the different rates of ascent with corresponding degrees of 

 vacuum ; and this might conveniently be done, as such variation of pressure scarcely, 

 if at all, affects the speed of the train ; this, in fact, is one of the great advantages 

 of the system, as the power expended in obtaining and keeping up the various degrees 

 of exhaustion will be in the direct ratio of the increase of ascent and no more. If it 

 occurs that an inclination intervenes, sharper than could be advantageously managed 

 in this way, a larger tube may be laid down in that particular length of the railway. 

 A remark was made that the atmospheric system might be applied to any existing 

 railway without interference with the mode of working with locomotive engines du- 

 ring the operation. 



A peculiarity of this system was explained by diagrams, to the following effect : — 

 Suppose the travelling load to be fifty tons, the degree of vacuum necessary to ob- 

 tain a given degree of velocity, producing a pressure of 10 lbs. per square inch on 

 the piston ; so long as the load is the same and the line level, the train will 

 move with equal velocity, because the speed is due to the rapidity with which the 

 air is pumped out of the pipe. But if the load be only twenty-five tons starting 

 with the same pressure as with fifty tons, the train then runs faster than the air is 

 drawn out of the pipe ; the power behind being so great in the first instance as to 

 force the load forward at an increased rate. But this does not last long ; the pump 

 going slower in proportion than the train, the air gets packed up, as it were, in front 

 of the piston, and becoming less rarefied offers greater resistance ; the velocity of the 

 train, which is very great at first, gradually diminishes until the amount of vacuum 

 becomes proportionate to the weight behind it, and then the train goes on uniformly. 

 Again, supposing the train to start with a load which is rather heavy, with a pressure 

 of only five or six pounds, the air is then drawn out quicker than the load can follow, 

 and makes the vacuum more perfect ; and thus the power increasing gradually, the 

 train increases its velocity until it becomes balanced with the vacuum. To ascend an 

 incline may be called equivalent to adding to the load, and to descend, equal to dimi- 

 nishing it ; when the train comes to an ascent it will reach the foot of the plane 

 with a considerable velocity ; but its rate will gradually decrease as it ascends, 

 until the power is brought up equivalent to the pressure, that is, until by the ex- 

 hausting-pump going faster than the train, a power is generated sufncienj to drive 

 it up the hill. In coming down hill, the trains will start at the top with very great 

 velocity ; but the air will immediately begin to act in front as a buffer until the 

 pressure is reduced. The moment the train comes to the level, its velocity will 

 immediately increase ; and thus the speed is nearly uniformly regulated, whatever 

 may be the inclination. 



In entering into the question of the cost of the atmospheric railway, several tables 

 were referred to, and it was distinctly and unreservedly stated that from £ 10,000 to 

 £ 12,000 per mile was sufficient to construct a line on this principle in most parts of 



