ON INSTRUMENTS FOR MEASURING THE SPEED OF SHIPS, 255 
are commonly met with in ships. For it is at once seen that, at a length of 
50 feet, the decrease (with increasing length) of the friction per square foot 
of every additional length is so small that it will make no yery great difference 
in our estimate of the total resistance of a surface three hundred feet long, 
whether we assume ‘such decrease to continue at the same rate throughout 
the last two hundred and fifty feet of the surface, or to cease entirely after 
fifty feet ; while it is in effect certain that the truth must lie somewhere 
between these two assumptions. 
Second Report of the Committee for the Selection and Nomenclature of 
Dynamical and Electrical Units, the Committee consisting of Professor 
Sir W. Tomson, F.R.S., Professor G. C. Fostrr, F.R.S., Professor J. 
Crerk Maxwett, F.R.S.,G. J. Stonny, F.R.S., Professor Firmmine 
JenxKIN, F.R.S., Dr. C. W. Simmens, -.R.S., F. J. Bramwetn, 
F.R.S., Professor W. G. Apams, F.R.S., Professor Batrour 
Stewart, F.R.S., and Professor Evernrt (Secretary.) 
Tae Committee on the Nomenclature of Dynamical and Electrical Units have 
circulated numerous copies of their last year’s Report among scientific men 
both at home and abroad. 
They believe, however, that, in order to render their recommendations 
fully available for science teaching and scientific work, a full and popular 
exposition of the whole subject of physical units is necessary, together with 
a collection of examples (tabular and otherwise) illustrating the application 
of systematic units to a variety of physical measurements. Students usually 
find peculiar difficulty in questions relating to units; and even the experi- 
enced scientific calculator is glad to have before him concrete examples with 
which to compare his own results, as a security against misapprehension or 
mistake. 
Some members of the Committee have been preparing a small volume of 
illustrations of the C. G. 8. system [Centimetre-Gramme-Second system] 
intended to meet this want. 
On Instruments for Measuring the Speed of Ships. Memorandum of 
Mr. Frovupr’s Experiments in relation to the Pressure-Log, with a 
Description of the Apparatus employed*. The Committee consists of 
W. Frovupe, F.R.S., F. J. Bramwewy, F.R.S., A.\E. Frercusr, 
Rey. E. L. Bertuon, James R. Napier, F.R.S., C. W. Merri- 
FIELD, F.R.S., Dr. C. W. Siemens, F.R.S., H.M. Brunet, W. Smita, 
Sir Witx1am Tuomson, F.R.S., and J. N, SHoonBrep. 
(Puates XIII. & XIV.) 
Ir seems best to begin by stating broadly the results which appear to have 
been established, reserving till afterwards the description of the apparatus 
and the details of the several experiments. 
* The experiments must be regarded as strictly elementary. 
