i88 THE POPULAR SCIENCE MONTHLY. 



is, the mean of all the hourly observations of each of these quantities 

 while in the square — is found and entered. Beside each is placed its 

 daily range, by which is to be understood the mean of the differences 

 between the daily maxima and minima for the number of days the 

 ship was in the square. 



Throughout a wide zone on both sides of the equator, the barom- 

 eter has a remarkably regular oscillation, attaining two maxima and 

 two minima every day. In order to discover the extent of this phe- 

 nomenon, the hours of its recurrence, and the amplitude of the alter- 

 nate rise and fall, the daily record of the barometer is carefully 

 examined, and, whenever the phenomenon is found clearly defined, 

 the hours of the two extreme lowest and two extreme highest read- 

 ings, together with the readings themselves, are noted and tabulated 

 on the blank. To save repetition, I will state here that all compila- 

 tions of the barometer are reduced to 32° Fahr. and sea-level. As 

 two more items of interest, the highest and the lowest readings of 

 the barometer and dry-bulb that occurred during the whole time the 

 ship was in the square are noted and entered. A miniature chart of 

 a five-degree square, but on a sufficiently large scale to allow of con- 

 siderable accuracy, is printed on the Form, for plotting the ship's 

 track : the position of the shij) being determined at 8 a. m., noon, and 

 8 p. M. of each day, these points afford the data for tracing the track. 

 Whenever currents exist, their set in points and their velocity in knots 

 and tenths of a knot per hour are written on this little chart at each 

 noon position ; an arrow is also projected from the track to indicate 

 their direction. At every noon the temperature of the sea- water at 

 the surface is very carefully taken, and entered on the chart on Form 

 B, beside the noon position of the ship ; it assists in coming to a con- 

 clusion as to the existence of currents. 



This completes the tabulated portion of the compilation on Form 

 B ; but, to unite the whole, to trace the connection of the several re- 

 lated quantities, and to describe such matters as could not be other- 

 wise noticed, ample remarks are made on the blank. 



Thus, at a glance, are all the observations of a ship in each square 

 visible on a single sheet ; it is not assumed that what she experienced 

 prevailed over all the expanse of the square ; her track lies before us 

 on the little chart that represents that square, and the tabulated obser- 

 vations beside it relate to that track only — a single line ! If we 

 have the observations and tracks of a large number of vessels, all over 

 every part of a five-degree square for each month — in other words, 

 if we have a multitude of sheets of Form B compiled — it is evident 

 that we can easily deduce the meteorological features of that square, 

 and judge whether they be like or dissimilar throughout its entire 

 extent. 



To follow up the fate of Form B, compilations having been made 

 on many thousand sheets of it from all the log-books and journals that 



