so long as the disk area, the surface, and pitch were properly adjusted to the speed of the vessel, and to enable the engines to use, at the maximum speed, just the full quantity of steam that the boilers can make, we have got pretty nearly as far as we can get.  To fix these dimensions of the propeller accurately at the present time, and without further knowledge of the action of the screw on the water, was, he thought, impossible.  All the rules and formulae are empirical.  The best one he knew is given in Table IV., due to Mr. Thom, the head of the Barrow Company’s engineering drawing office, and at present acting manager, who has used it for some years in practice.  These formulae are based upon the assumption that the area of propeller disk should be proportional to the indicated horse power, divided by the cube of the speed, and the same with the projected area of the propeller and also the surface.

TABLE IV.

Particulars of Propellers and Constants.

------------------------------+-------+---------+------

----+--------------
| Length|         |   Proj.  |  Feet per
Ship.             |   of  |  Disk   |   surf.  |   minute.
| ship. |constant.| constant.|Speed of tips.
------------------------------+-------+---------+----------+

--------------
City of Rome.                 |   542 |   220   |    69    |   4,715
Normandie                     |   459 |   250   |    66    |   4,099
Furnessia                     |   445 |   223   |    69    |   3,654
Eden                          |   300 |   211   |    64    |   3,080
Yorouba                       |   270 |   213   |    63    |   3,202
Taygete                       |   260 |   238   |    56    |   3,166
Kow-shing                     |   250 |   171   |    69    |   3,369
S.Y.  Monarch                  |   152 |   221   |    65    |   4,040
S.Y.  Aries                    |   138 |   179   |    56    |   2,986
Twin screw Fenella            |   200 |   244   |    64    |   2,890
Twin screw H.M.S.  Fearless[2] |   220 |   277   |    67    |   5,022
Twin screw H.M.S.  Iris        |   —–­ |   454[6]|   135[6] |    —–­
Twin screw H.M.S.  Iris [3]    |   300 |   412   |   221    |    —–­
Twin screw H.M.S.  Iris [4]    |   300 |   346   |    99    |   4,961
Twin screw H.M.S.  Iris [5]    |   300 |   439   |    82    |   5,309
------------------------------+-------+---------+----------+

-------------

  [Footnote 2:  Estimated with a speed of 17.5 knots and 3,370
  I.H.P.]

  [Footnote 3:  With the first propeller at the estimated speed of
  17.5 knots and 7,000 I.H.P.]

[Footnote 4:  With four bladed modified Griffith’s on actual
trial.]

[Footnote 5:  With two bladed modified Griffith’s on actual trial.]

[Footnote 6:  Constants obtained from first propeller calculated
from a speed of 18.5 knots and 7,500 I.H.P.