vessels with a moderate air pressure, to as much as 70 and even 80 lb per sq. ft. in the express types of boiler used in torpedo boats and similar craft. _Performance of Boilers._--The makers of several types of boilers have published particulars regarding the efficiency of the boilers they construct, but naturally these results have been obtained under the most favourable circumstances which may not always represent the conditions of ordinary working. The following table of actual results of marine boiler trials, made at the instance of the British admiralty, is particularly useful because the trials were made with great care under working conditions, the whole of the coal being weighed and the feed-water measured throughout the trials by skilled observers. The various trials can be compared amongst themselves as South Welsh coal of excellent quality was used in all cases. In experimental tests such as those above referred to, many conditions have to be taken into account, the principal being the duration of the trial. It is essential that the condition of the boiler at the conclusion of the test should be precisely the same as at the commencement, both as regards the quantity of unconsumed coals on the fire-grate and the quantity of water and the steam-pressure in the boiler. The longer the period over which the observations are taken the less is the influence of errors in the estimation of these particulars. Further, in order properly to represent working conditions, the rate of combustion of the fuel throughout the trial must be the same as that intended to be used in ordinary working, and the duration of the test must be sufficient to include proportionately as much cleaning of fires as would occur under the normal working conditions. The tests should always be made with the kind of coal intended to be generally used, and the records should include a test of the calorific value of a sample of the fuel carefully selected so as fairly to represent the bulk of the coal used during the trial. The periodic records taken are the weights of the fuel used and of the ashes, &c., produced, the temperature and quantity of the feed-water, the steam pressure maintained, and the wetness of the steam produced. This last should be ascertained from samples taken from the steam pipe at a position where the full pressure is maintained. In order to reduce to a common standard observations taken under different conditions of feed temperatures and steam pressures, the results are calculated to an equivalent evaporation at the atmospheric pressure from a feed temperature of 212 deg. F. (J. T. Mi.) TRIALS OF VARIOUS TYPES OF MARINE BOILERS