REPORT OF COMMISSIONER OF FISH AND FISHERIES. 131 



uiifortiuiately, through the hick of sufficieut means the Signal vSeivice 

 was obliged, in the latter part of 1890, to discontinue its cooperation in 

 regard to this important subject. 



During October, 1889, Prof. Libbey, with the steamer Fish Hatck, 

 visited nearly all of the temperature light- stations located between 

 Cape Cod and Chesapeake Bay, and insi)ected the thermometers used 

 in making the observations, also instructing the attendants as to the 

 projjer way of reading and caring for them. All 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 it is intended shall be introduced 

 at an early date. The stations visited were as follows : Pollock Rii^, 

 Nantucket New South Shoal, Vineyard Sound, Brenton Eeef, 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 Eeport 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 00° F. for the 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 difter- 

 ence being in their graduation. 



In the future, moreover, the observations will be reduced to 15"^ C, 

 instead of 60^ F., 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 Fish JIaivk on the oyster-grounds of the Atlantic coast. 



