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REPORT OF COMMISSIONER OF FISH AND FISHERIES. 131 
unfortunately, through the lack of sufficient means the Signal Service 
was obliged, in the latter part of 1890, to discontinue its codperation in 
regard to this important subject. 
During October, 1889, Prof. Libbey, with the steamer Fish Haak, 
visited nearly all of the temperature light-stations located between 
Cape Cod and Chesapeake Bay, and inspected the thermometers used 
in making the observations, also instructing the attendants as to the 
proper way of reading and caring for them, Ail instruments were com- 
pared with a standard, and those showing any appreciable variation 
were replaced by new ones. Prof. Libbey suggests several changes in 
respect to this branch of work, which itis intended shall be introduced 
at an early date. The stations visited were as follows: Pollock Rip, 
Nantucket New South Shoal, Vineyard Sound, Brenton Reef, Block 
Island, Sandy Hook, Five Fathom Bank, and Winter Quarter Shoal. 
Changes in density observations.—The hydrometers which have been 
used by the Fish Commission, as well as by the U. S. Coast and Geo. 
detic Survey, for determining the density of sea water are the so-called 
Hilgard salinometers, consisting of an elongate glass float and stem, the 
scale being marked upon the latter. They are described and figured 
in Appendix 16 of the Coast Survey Report for 1874. Up to the pres- 
ent time the graduation of the scale has been referred to pure water at 
60° F., and the observations have been reduced by means of the Hub- 
bard table to a uniform temperature of 60° EF. forthe purposes of compar- 
ison. For certain reasons, however, it now seems advisable to change 
the former standard by making it conform to the temperature at which 
pure water attains its maximum density, and 4° C., the nearest inte- 
ger to that temperature, has, for convenience sake, been adopted as the 
future standard. Upon this basis the observations will conform more 
closely with modern European methods. This change was agreed upon 
by the Superintendent of the Coast Survey and the Commissioner of 
Fisheries during the winter of 1889-90, but some delay must ensue in 
the preparation and the introduction of the new instruments, which will 
be constructed upon the same patterns as the old ones, the only differ- 
ence being in their graduation. 
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In the future, moreover, the observations will be reduced to 15° C., 
instead of 60° I*., both of these temperatures, however, being approx- 
imately identical, and a convenient table for this purpose, prepared by 
Mr. O. H. Tittmann has been published in Bulletin No. 18 of the Coast 
Survey for 1890. This table also gives a constant by which the reduc- 
tions of observations obtained with the old instruments may be made 
to conform to the new standards. 
Other physical inquiries are discussed in connection with the opera- 
tions of the steamer Albatross in the north Pacific Ocean and of the 
steamer Mish Hawk on the oyster-grounds of the Atlantic coast. 
