60 Lake Maxinkuckee, Physical and Biological Survey 



THE Am 



Pressure: The data concerning air pressure at Lake Maxin- 

 kuckee were obtained by readings taken 3 times daily, at 6 a. m., 

 noon, and 6 p. m., from a compensated aneroid barometer kept 

 hanging on a porch of the cottage used as our laboratory. The 

 readings were continued from July 25, 1900, to June, 1901. The 

 average pressure during that time was 29.291 inches. The mini- 

 mum pressure recorded during that period was 28.62 inches, taken 

 at noon of March 8, 1901, and the highest pressure noted was 

 30.26 inches on January 3, 1901, about 6 a. m., giving a range of 

 1.64 inches. A self-recording instrument would in all probability 

 have given a lower minimum, a higher maximum, and larger range. 

 The average pressure did not vary greatly during the different 

 months of the year. The month having the lowest average was 

 October, with an average of 29.005, and that having the highest 

 was February, with an average pressure of 29.583. The month 

 having the least range was August, in which the pressure varied 

 from 29.42 to 29.85, exhibiting a variation of .43 inch, and the 

 month showing the greatest range was January, with a range of 

 from 28.82 to 30.26, or 1.44 difference. The greatest change of 

 the barometer noted within the space of 6 hours was a fall of .9 

 inch between noon and 6 p. m. on May 2, 1901, and the greatest 

 change in the same direction for a single period of 24 hours was 

 from 29.85 on the evening of September 14 to 28.88 on the even- 

 ing of September 15, making a fall of .97 inch. The greatest 

 increase of barometric pressure between two consecutive observa- 

 tions was from 28.91 at noon of May 21 to 29.77 at 6 p. m., a 

 rise of .86 inch, and this was followed by an almost equal fall 

 within the next 12 hours. It not infrequently happened, espe- 

 cially during the month of August, 1900, that 2 successive read- 

 ings were the same, or nearly the same, and in nearly all cases 

 where this occurred the two nearly equal or equal readings were 

 those of noon and evening, there being usually little change during 

 the afternoon. The period of 24 hours showing the least change 

 was from noon August 14 to noon August 15, during which the 

 change was only .08 inch. 



In the study of the barometric readings at the lake these were 

 plotted in a graph (the time periods being represented by abcissas 

 and the height of the barometer in inches by ordinates) and the 

 graph so constructed exhibited at a glance the most striking 

 features of the barometric record. Of these the following may be 

 noted : 



