Miscellaneous. 473 



gauges several times daily, and occasionally every hour of the day 

 and night, from the 1st of April to the 20th of July. 



A gauge was attached to a sugar-maple, March 31st, which was 

 three days after the maximum flow of sap for this species, so that 

 further observations are required earlier in the season to complete 

 the record and determine with certainty the maximum pressure 

 Avhich it exliibits in the spring. Of the record made, the follow- 

 ing facts are specially interesting : first the mercury was subject to 

 constant and singular oscillations, standing usually in the morning 

 below zero, so that there was indicated a powerful suction into the 

 tree, and rising rapidly with the sun until the outward pressure 

 was sufficient to sustain a column of water many feet in height. 

 Thus at 7 A.M., April 21st, there was a suction into the tree suf- 

 ficient to raise a column of water 25-90 feet. As soon as the 

 morning sun began to shine on the tree the mercury suddenly 

 began to rise, so that at 9.15 a.m. the pressure outward was enough 

 to sustain a column of water 18-4:7 feet high, a change represented 

 by more than 44 feet of water. On the morning of April 22nd the 

 change was still greater, requiring for its representation 47-42 feet 

 of water. These extraordinar}!- fluctuations were not attended by 

 any peculiar state of the weather, and happened twelve days before 

 there were any indications of growth to be detected in the buds. 

 These observations are believed to be quite new, and as yet in- 

 explicable, but will receive further attention another spring. 



The maximum pressure of the sap for the season was observed 

 at 10 A.M., April 11th, and was equal to sustaining a column of 

 water 31-73 feet high. This was an excellent sap day, considering 

 the lateness of the season. There was noticed a general corre- 

 spondence between the flow of sap in other maples and the pressure 

 on the gauge. 



After April 29th the mercury remained constantly below zero, 

 day and night. During the month of May there was a uniform 

 suction equal to about 8 feet of water; and the unaccountable 

 feature of this fact is, that, though apparently produced by exhala- 

 tion from the expanding leaves, it remained the same, day and 

 night, for several weeks. In June the suction gradually lessened, 

 and finally disappeared, the mercury standing steadily at zero. 



On the;^Oth of April two gauges were attached to a large black 

 birch — one at the ground, and the other 30 feet higher. The next 

 morning at six o'clock the lower gauge indicated the astonishing 

 pressure of 5()-G5 feet of water, and the upper one of 20-74 feet. 

 The difference between the indications of the two gauges was 

 thus 29-91 feet, while the actual distance between them was 

 30-20 feet, so that it corresponded almost exactly as if they were 

 connected by a tube. In order to learn whether the same principle 

 would prevail if the upper gauge was moved, it was raised 12 feet 

 higher. The same correspondence continued tlirough nearly all tho 

 observations of the season, notwithstanding the gauges were sepa- 

 rated by 42-20 feet of close-grained birch-wood. 



At 12.30 P.M., April 21st, a hole was bored into the tree on the 

 side opposite to the lower gauge, and at the same level. Both 



Ann. & Mag. N. Hist. ^cr. 4. VJ. xiii. 34 



