376 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
NAVIGATION: APPARATUS AND METHODS. 
Tbe principal implements used in tlie navigation of the vessel comprise three 
Negus and one Bliss & Creighton box chronometers, the latter being used as a hack; 
also a comparing watch. The Ritchie liquid comj)asses are used for standard, 
steering, telltale, and boat service. The standard comiiass has an azimuth circle and 
alidade, and another is fitted with tripod and circle. A j)elorus is provided for taking 
bearings of objects which can not be seen from the standard. The usual number of 
sextants and octants are provided; also an artificial horizon. 
The Bliss and Waller taffrail logs are used to measure the vessel’s speed through 
the water, and the common hand-lead measures the depths within its capacity, while 
the Tanner sounding machine, either alone or with the Bassnett atmospheric sounder, 
or Sir William Thomson’s tubes attached, is used in deeper waters. Both telescopic 
and binocular marine glasses are provided, and for convenience in platting there is 
a three- arm protractor, a Negus course-indicator, Sigsbee’s parallel rulers, drawing 
instruments, etc. 
The chronometers are placed ttnder a lounge in the chart room, the transporting 
cases being screwed to a false bottom on the deck. In this position they are secure 
from shocks, and the top of the lounge, opening and shutting on hinges, fits tightly 
enoirgh to i>revent drafts of air or any great changes of temperature. The most pow- 
erful disturbing element on the rates of the chronometers has been the vibration of the 
hull, caused by the dynamo engine, which is usually in operation from dark until 11 
p. m. They appear to run equally well together while this vibration takes place every 
day, and during any material interval that it does not take place at all; but an 
interruption of either state of repose or vibration is almost invariably accompanied by 
a change in the record differences in tlie daily comparison book, showing that their rates 
are temporarily disturbed. 
On reaching port the chronometers are rated as soon as possible by comiiarison 
with the time obtained by telegraphic connection with some observatory clock; or, 
when such connection is not possible, equal altitudes of the sun are taken, and the 
errors corrected back if the discrepancy is greater than the probable limits of 
personal and instrumental errors of observation and platting. 
The standard compass is ])laced about 15 feet forward of the smokestack, on the 
deckhouse, where it was located by a magnetic survey; it was found that in this 
position the needle was least disturbed by the various magnetic forces exerted by the 
metal of and in the ship; it is also in a convenient position for use, being handy for 
taking bearings and under the eye of the officer of tlie deck when under way. 
The standard compass is not compensated, and the local deviation is obtained by 
swinging ship under steam, observing azimuths of the sun on every point, making 
a circle with port helm, then with starboard, the mean of the results being accepted as 
coi’rect. The curve of deviations being platted upon a Napier diagram, a table of 
magnetic courses is deduced for convenience in laying the ship’s head. 
The heeling error is obtained by listing the vessel to starboard and port and 
observing azimuths of the sun as before. 
In general terms it may be stated that the changes of deviations due to inclination 
are such that when heeled to starboard the ship’s head is thrown to windward, or 
toward the higher side, when on any course in the northern semicircle; in the southern 
