XIX -EXPERIMENTS UPON THE TIME OF EXPOSURE REQUIRED 

 FOR ACCURATE OBSERVATIONS WITH THE CASELLA-MILLER 

 DEEP-SEA THERMOMETER. 



By Commander L. A. BexVRDslee, U, S. N. 



United States Steamer Blue-light, 



NomiJc, Conn., September 1, 1874. 



Sir : In compliance with your request that I should examine and 

 compare the thermometers, standards and others, belonging to the United 

 States Fish Commission, I have carried on a series of experiments with 

 them, the results of which 1 herewith submit to you as one of the results 

 of the summer's work of the Commission. 



The instruments delivered by you to me to examine were the follow- 

 ing, arranged and numbered according to their sensitiveness as devel- 

 oped during experiments: 



No. i. A mercurial standard, made by L. Casella, of London, No. 7,432, 

 reading from zero up to 120°, on a scale marked on the glass, and twelve 

 inches loug, giving ten degrees to the inch ; bulb cylindrical, .75 of an 

 inch in length. No mounting; sensitive to the slightest change, and 

 rapid in action. 



No. 2. A mercurial standard, No. 16,578, made by James Greene, New 

 York, reading from zero up to 120°, on a scale marked on the glass, and 

 four and four-tenths inches long, giving twenty-seven and two-tenths 

 degrees to an inch ; bulb cylindrical, seven-tenths of an inch in length. 

 No mounting; as sensitive as No. 1, and agreeing closely with it. 



No. 3. A mercurial standard, no number, made by James Greene, New 

 York, reading from 50° up to 105"^, on a scale of six inches, marked upon 

 a metal-back mounting. Very sensitive, but not convenient, on account 

 of limited range. 



No. 4. A mercurial standard, no number, made by Tagliabue, of New 

 York, reading from 5° below zero up to 125°, on a scale 7.8 inches long, 

 equal to nearly 16° to an inch ; scale marked on a metal-back mounting; 

 bulb spherical, with a brass guard. Moderately sensitive, but slow in 

 action. 



No. 5. A United States Navy mercurial thermometer, mounted with 

 metal back and cap guard; spherical bulb; scale marked on bacii. 

 Moderately sensitive, and fair in action. 



No. 6. A Casella- Miller self-registering deep-sea thermometer, No. 

 15,720. 



No. 7. The same. No. 17,017. 



