18 
EXPERIMENTS. 
The operation of replacing the screw requires more skilful management. For 
this purpose the chain or rope b is let out to a known distance, and there fixed, so 
that by pulling equally at dd the axis is brought to its proper place in the dead 
wood; when the holding-down bolts are forced down, and secure the bearings as 
before. To ensure success in this operation, however, it is clear we must have calm 
weather, and the axis must not be so far below the surface of the water but that a 
man can reach it with his hands, as well to bring the bearings exactly in place in 
case of the chains failing to do so, as to disengage them when the operation is 
completed. In bad weather it is obvious that a heavy body like the screw, 
suspended by chains, and out of sight, will be too unmanageable to admit of this 
operation being safely performed; and until some more certain process is proposed 
we can only hope to be able to ship and unship the screw in calm weather, or 
have recourse to it as a desperate measure in order to avoid some greater evil. 
To possess the means of removing or replacing the screw, however, even under 
the difficulties we have named, is too obvious an advantage to allow of such a 
provision ever being omitted; but a more efficient and secure method of effecting 
so desirable an object will be a valuable improvement. 
EXPERIMENTS. 
The first experiments were made with a view to determine the speed of the 
Archimedes in smooth water. For this purpose various trials were made at a 
point called the “ measured mile,” in Long Reach, and her mean speed was 
ascertained to be 9'64 miles per hour. But as it was to sea-going vessels that 
the screw was at first considered to be peculiarly adapted, so soon as all was 
complete the vessel made several voyages, the results of which appear to have 
been highly satisfactory. On application being made to the Admiralty, it was 
ordered that a series of trials should be undertaken to and from Dover with 
Her Majesty’s steam packets belonging to that port, and Captain Chappell, R.N., 
was deputed to report thereon, and to institute such other experiments as he might 
deem necessary. Before Captain Chappell’s arrival, however, several interesting 
trials were made, a log of which was kept by Captain Burridge, R.N. (who was 
on board the Archimedes during the trials), and from which we make the following 
extracts: 
“ First day, April 21, 1840; light breezes from the northward. 
A. M. 
7 30. Left Dover Roads with Her Majesty’s steamer Ariel for Calais; Archimedes 
rather leading. 
8 45. Both vessels made sail; light wind from S.W.