218 ~ REPORT—1858. 
The mean rate of the tide, therefore, was about 1°46 knot, the speed of the vessel 
through the water about 8°78 knots, and the mean slip about 18°42 per cent. From 
these data may be deduced the following relations, viz. :— 
That the direct thrust of the screw against the tide is 6877 lbs., and the resultant 
4429, and the slip, being the difference of the ratio of the square roots of these 
quantities, is therefore 19°75 per cent. 
That the direct thrust with the tide is 6498 lbs., and the resultant, as before, 4429 ; 
the slip is 17°44 per cent. 
The mean slip is, consequently, 18°59, which is sufficiently near the former calcu- 
lation of 18°42. 
A further deduction is—that the resultant, 4429 lbs., is at least equal to, or 
greater than, the specific resistance; for, if not, the slip would not have approached 
so close to the theoretic ratio which, as before stated, was calculated before the 
trial took place. 
This principle of the slip may be used to correct the speed of the Undine in her 
run from Holyhead to the Mull of Cantire, when, with smooth water and light airs, 
she had the tide with her the greater part of the time. 
The results were as under, viz, :— 
Indicator horse-power .........sesceecrears 158°77 
‘Revalatans nent cles paeteve ce okt a7 ercasdtiged, ccotale Wlons ‘ 98°40 
Speed of yessel......... A sie ratner ia Mee eeR Lets 9°97 knots (by land). 
i screw ..... Bice ten lnts MEMO a areal ste ae 11°06 
SiN crash oid pRetirse SDA Recs Seca ain ie at 9°24 per cent. 
Assuming the standard ratio of slip, as before determined, at about 18 per cent., 
the tide appears to have advanced the speed of the vessel about a mean rate of 0°87 
of a knot per hour, and therefore reducing the speed through the water to 9°] knots, 
or 0'16 of a knot slower than at the measured mile, the indicator horse-power being 
1°68 greater. 
' The Undine was, it is believed, deeper in the water on this last occasion. 
The following questions arise for solution by means of the experiments which it is 
my object to procure to be conducted at sea :— 
In any given vessel, what relations obtain between the resistance due to her sec- 
tion in smooth water and calm weather, and the resistances the vessel herself 
experiences under various conditions, when under sail, under the screw, and under 
both? ae 
' What are the relations in any giyen engine of absorbed power at different speeds ? 
In any given screw, what are the relations between its length and its speed of 
rotation, so that a continuous disc shall be maintained ? and what immersion in rela- 
tion to the diameter is necessary to this result ? 
What are the relations between the direct thrust of any given disc and its resultant, 
and the consequent effective area and pitch and ratio of slip ? 
Researches of this nature, if carefully conducted, will show that the screw is 
capable of more accurate application, and more extended use, than has yet been 
made of it. Its slip is a calculable element, provided the periphery be so immersed, 
and the rotation such that a continuous disc is maintained. 
The limits of immersion and rotation are yet to be determined. 
On a proposed Floating Lighthouse. By Josrrn Joun Murpuy. 
On a new Double-acting Steam Hammer. By Witt1am Naytor, late of 
Norwich, now of 3 New Broad Street, London, E.C. 
In considering the principle of the double-action steam hammer, we may draw 
some analogy with the steam gun for throwing projectiles, and assume the cylinder 
to be as the gun, and the piston and hammer attached as the ball. Let us assume 
the cylinder as one foot in length, with the top cover off, and the relative force of 
steam to the weight of the hammer such as by the time the piston reached the top 
of the cylinder, and should be moving at a velocity of 32 feet per second, it would 
ascend above the cylinder 16 feet, and when it had returned 16 feet by gravity it 
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