PHYSICAL INVESTIGATIONS OFF THE NEW ENGLAND COAST. 397 
and the necessary therniometers taken from the tray below. The bottom space was 
filled with thermometers held in reserve in case of accidents occurring, but it was 
never opened except to care for the thermometers. 
INSTEUMENTS FOE SPECIFIC-GEAVITY OBSEEVATIONS. 
These observations were made with the Hilgard ocean salinometer. The specimens 
of water from the surface were obtained in the ordinary manner. The specimens from 
the bottom or from any desired depth were obtained by means of a Sigsbee water-cup. 
INSTRUMENTAL CORRECTIONS, REDUCTION OF OBSERVATIONS, ETC. 
The specific-gravity observations, made with the Hilgard salinometer, were reduced 
by means of the table given for that purpose in the original description of the instru- 
ment, as published in Appendix 16 of the H. S. Coast Survey Report for 1874, and 
found on page 155 of that volume. This table may also be found on page 78 of the 
Report on the TJ. S. Fish Commission steamer Albatross \\\ the Annual Report of the 
Commissioner of Fish and Fisheries for 1883, and is again reproduced below with an 
alteration to be noticed immediately. It is based upon the observations of the 
expansibility of sea water made by Prof. J. S. Hubbard, U. S. Navy. In making use 
of this table Professor Rockwood’s attention was at once attracted by the irregularity 
in the resulting corrections for temperature between 59° and 61°, and further exami- 
nation led him to conclude that the tabular number for 60° was erroneous and should 
be 0.000125 instead of 0.000000. This conclusion being concurred in by Mr. O. H. Titt- 
mau, of the Bureau of Weights and Measures of the U. S. Coast and Geodetic Survey, 
the table as given diliers from the original table by the substitution of 0=p .000125 for 
-f 0.000000 as the tabular number for 60°, where the minus sign is to be used with tem- 
peratures below 60°. To facilitate the use of the table the following directions are 
given : 
Record the actual observation of hydrometer and thermometer. From column II take the number 
corresponding to the observed temperature and multiply this number by the number of degrees and 
fractions of a degree that the observed temperature differs from ti0°. Apply this product as a correc- 
tion, with proper sign, to the reading of the salinometer and the result will be the reading of the 
salinometer at the standard temperature of 60° F. 
Temp. 
Correction 
for reduction 
to 600 Y. 
Teuip. 
Correction 
for reduction 
to 60° F. 
Temp. 
Correction 
for reduction 
to 60° F. 
Temp. 
Correction 
for reduction 
to 60° F. 
I. 
II. 
I. 
II. 
I. 
II. 
I. 
II. 
o 
o 
o 
O 
50 
—0. 000108 
60 
+ 0. 000125 
70 
4-0. 000145 
80 
4-0. 000158 
51 
— 0. 000110 
61 
-f 0. 000130 
71 
4-0. 000146 
81 
-f 0. 000159 
52 
— 0. 000112 
62 
-1-0. 000136 
72 
4-0. 000147 
82 
4-0. 000160 
53 
—0, 000113 
63 
-1-0. 000137 
73 
4-0. 000148 
83 
4-0. 000162 
54 
— 0. 000115 
64 
-1-0. 000137 
74 
4-0. 000149 
84 
4-0. 000163 
55 
—0. 000118 
65 
-1-0. 000138 
75 
-f-0. 000151 
85 
4-0. 000164 
56 
—0. 000120 
66 
-fO. 000140 
76 
4-0. 000152 
86 
-j-0. 000166 
57 
—0. 000120 
67 
4-0. 000141 
77 
4-0. 000154 
87 
4-0. 000167 
58 
—0.000120 
68 
-fO. 0001*42 
78 
4-0. 000156 
88 
-f 0. 000168 
59 
—0. 000120 
69 
4-0. 000143 
79 
-f 0. 000157 
89 
-f-0. 000170 
But as it was desired to employ 4° C. as the standard temperature instead of 60° 
F. and that the reductions be made to 15° C. in place of 60° F., a further correction 
was necessary. This correction is constant, and its amount as determined by Mr. O. 
