66 APPENDIX. 



where from the length of a voyage there is a difficulty in carrying a sufficient supply of fuel, 

 great economy will be effected by the sacrifice of some speed. 



This, perhaps, with the present engines, cannot be more effectively done than by the mode 

 adopted by Mr. Barlow, in his experiments on the Lightning ; viz. working the steam at a 

 very little pressure above the atmosphere : this, in fair weather, when the engine can make 

 nearly its full number of strokes, will produce a very small diminution of speed ; and in 

 circumstances when any additional power may be required for the safety and management 

 of the vessel, it can be at once effected by the addition of a weight to the safety valve. 



By referring to the experiments on the Lightning, it will be seen, that the increase of speed 

 by the additional pressure of steam in the boiler is much less in proportion to the fuel con- 

 sumed, than the theoretical law would give it, chiefly owing, probably, to the vacuum in the 

 condenser being so much less perfect in this case, so that the effective power is less than in 

 the proportion of the consumption of steam : this is an additional argument in favour of 

 working at a low pressure in sea boats ; and there will be, besides, less wear of the engine 

 and less liability to get out of order. 



It is however a very commonly received opinion, totally at variance with the above results, 

 that by increasing the power in proportion to the tonnage, less fuel would be consumed in a 

 voyage of a given length. In fact, Dr. Lardner, in his work on the Steam Engine, states, 

 " that the results pf experience obtained in the steam navigation of our channels, and parti- 

 cularly in the case of the Post Office packets on the Liverpool station, have clearly established 

 the fact, that by increasing the ratio of the power to the tonnage, an actual saving of fuel in a 

 given distance is effected ;" which anomaly he accounts for by the diminution of the draught 

 of water produced by the additional speed. 



The question of the most economical ratio of the power to the tonnage being one of the 

 highest importance in vessels destined for long voyages, we have endeavoured to obtain as many 

 facts and experiments as possible, of the times of making sea voyages of various vessels, with 

 the tonnage and hors'e power ; and, it is found, in every instance, that the consumption of fuel 

 is less the smaller the power in proportion to the tonnage. 



To illustrate the above, we give the following table, from the Parliamentary Reports on 

 Steam Navigation to India, of the times of the voyages of Her Majesty's Admiralty steamers 

 to Corfu and Patras, and back, a distance of 5200 miles, made by nine different vessels, 

 varying in tonnage and horse power. These voyages being so extensive, and made in every 

 variety of weather, we have chosen them as furnishing the best possible data by which to 

 ascertain the truth of the above question. 



The columns of the table, 1, 2, 3, 4, 5, and 7, are abstracted from the Parliamentary Report 

 as thev stand ; the remaining columns are calculated. Column 6 is the number of tons per 

 horse power, obtained by dividing the measured tonnage by the nominal horse power. Co- 

 lumn 8 is the time of steaming in each voyage, obtained from column 7 by subtracting the 

 time of stoppages from that of the whole, voyage. Column 9 gives the means of the preceding. 

 Column 10 is the actual consumption of coals during the voyage, calculated at the rate of 

 8 Ibs. per horse power per hour ; which (as stated by Mr. Field in his examination) is found 

 to be very nearly the average of all engines. Column 1 1 is obtained by dividing the whole 

 consumption by the tonnage, and gives the weight per ton consumed during the voyage, and 

 consequently expressing the relative economy of each vessel. 



