xxxvin 



INTRODUCTION. 



and the linear expansion of steel for one degree Fahrenheit being .0000060, the correction due 

 to alterations of the measuring rod will be 



.0000060 ( 32) h. 



The following table contains the corrections used in the reductions, and which were com- 

 puted by the preceding formulas for a mean height of the barometer of 28.0 inches: 







TABLE VI. 



Corrections applied to readings of the barometer to reduce the observations to 32 Fahrenheit. 



THERMOMETERS. 



All the thermometers, except that attached to the barometer and the self-registering for 

 radiation to the sky, were enclosed within boxes of light boards, open at the bottom, and sus- 

 pended under a balcony on the south front of the house. These enclosing boxes cut off radiant 

 and reflected heat from opposite walls and roofs, whilst their construction permitted free circu- 

 lation of air about the bulbs. They were hung at the height of the observer's eye, within a 

 space of five feet, and about twenty feet above the level of the street. In order to avoid direct 

 action of the sun upon them during a part of the summer months, it was necessary to remove 

 the thermometers to the north side of the house for the 6 P. M. observations, and they remained 

 there until after the 6 A. M. records. The dates of the removals are duly entered in the 

 journals. 



Standard thermometer. The temperature of the air was noted by a standard thermometer 

 made by Henry Barrow & Co., London. Its scale is of silvered brass, 14.8 inches in length, 

 and is apparently divided with care to 0.5 Fahrenheit, from 43 to -f- 232. It is enclosed 

 in a mahogany case with a sliding front of glass, which last was removed when the thermo- 

 meter was suspended within the outer box. 



Wet and dry bulb thermometers. The psychrometer used was made by Bunten, of Paris. 

 Each thermometer tube is enclosed within a cylinder of glass twelve inches in length, the lower 

 extremity of which is joined to the tube by fusion. The upper ends of the cylinders are closed 

 with ferrules and caps of brass, and one is suspended on each side of a wooden upright fitted 

 with a heavy metallic base. The centigrade scales, divided on paper to 0.2, from 5 to 

 + 32, are enclosed within the cylinders. A table of Fahrenheit equivalents was computed 

 and inserted in the journal for immediate reference. 



