These vessels, which are nearly uniform in size and speed, were designed and built with a view of affording the public an extra supply of steamers, such as would best attain the three-fold purpose of safety, speed, and comfort; and certainly their performances have realised the objects and expectations of their enterprising owners. Built of iron with watertight and fire-proof compartments, they afford in their strength every guarantee for safety, nor are their owners behind their rivals in the caution exercised to avoid the ordinary dangers of rapid navigation.[253] But speed with them, as with all well-regulated navigation companies, appears to be only a secondary consideration, for, not satisfied with a general regulation, Messrs. Ismay and Imrie, in their own interest, as well as in that of the public, have wisely issued to the commanders of their ships a special manuscript letter[254] reminding them, in the most distinct manner, that the safety of the ship under their charge and of all on board of her must ever be their first consideration. That their ships have attained an average rate of speed hitherto unrivalled, combined with great regularity, may be seen by their logs.[255] Their _Adriatic_[256] has far surpassed the famous American steamship of that name which once belonged to the Collins line, she having attained the extraordinary speed of 455 statute miles in one day.[257] Nor has the comfort of the passengers been in any way neglected. [Sidenote: _Britannic_ and _Germanic_.] At page 278 I furnish a drawing of their newest vessel; and for the information of my nautical readers I may state that the _Britannic_ and _Germanic_[258] are similar in all respects. These vessels were built of iron by Messrs. Harland and Wolff, Belfast.[259] [Sidenote: Their great speed.] The engines of the _Britannic_ are by Maudslay, Sons, and Field; they are 760 nominal, but indicated 5090 horse-power on the trial trip. They have four inverted cylinders, the high pressure above the low; the diameters of the cylinders are 48 inches and 83 inches respectively, and the length of stroke 5 feet. The pressure of steam is 70lbs. per square inch, and the boilers, eight in number, are fired at both ends with thirty-two furnaces. The propeller has four blades, and is 23 feet 6 inches in diameter, with 28 feet to 31 feet 6 inches pitch. The mode of lifting the screw is novel, as may be seen by the drawing on the following page. [Sidenote: Details of _Britannic_, and form of her screw.]