312 



Mr. Knight, it must pass the cellular substance ; and to show that 

 the cellular substance is pervious to fluids, he quotes an instance 

 from a preceding communication, in which bark was generated on 

 the surface of the cellular substance of pollard oaks. A new expe- 

 riment is also related in confirmation of this opinion. Various branches 

 of two years old were cut from different trees ; and after the cut 

 surface had been covered with a cement impermeable to water, a 

 portion of the bark was detached from each, so as to expose the sur- 

 face of the alburnum. They were then immersed in coloured infu- 

 sions for twenty hours, and were found to have imbibed the colour 

 between the alburnous tubes, apparently through the cellular sub- 

 stance. 



When an incision is made into the alburnum near the root, and 

 sap is seen to flow from it, it may be observed to run even more 

 abundantly from the upper surface of the incision ; and since the 

 quantity which exudes is full a hundred times more than was pre- 

 viously contained in the alburnous tubes, it appears evident that it is 

 raised through some other channel. 



Mr. Knight concludes, therefore, that the sap ascends through the 

 cellular substance, and conceives that part to be so organized as to 

 permit the sap to escape more readily upioards than in any other di- 

 rection ; and, by its alternate contraction and expansion, to be fully 

 capable of propelling the sap with all the impulse which it is known 

 to have in the spring. 



The alburnous tubes appear to the author to answer also another 

 purpose, since their cylindrical form occasions the strength of the 

 materials employed to be the greatest possible. 



The author concludes by observing, that though he retracts an 

 opinion formerly entertained respecting the ascent of sap through the 

 alburnous tubes, yet his opinions concerning its subsequent motion 

 through the central vessels, leaves, and bark, remain unchanged. 



Eclipses of the Satellites of Jupiter, observed by John Goldingham, 

 Esq. F.R.S. and under his Super intendance, at Madras, in the East 

 Indies. Read June 30, 1808. [Phil. Trans. 1808, p. 322.] 



Mr. Goldingham's observations are prefaced by a short account of 

 the instruments employed, and some general remarks upon the cir- 

 cumstances necessary to be attended to, in drawing inferences from 

 them. Two telescopes were employed, both made by Dollond, of 

 85 feet focal length, with a magnifying power between 70 and 80 ; 

 and the time observed by a good clock, with gridiron pendulum, was 

 deduced from the transit of the sun nearest to the eclipse, and veri- 

 fied by the next preceding or following transit. 



The longitude of the place of observation is given, as determined 

 from numerous observations of various kinds, that it may be com- 

 pared with that deduced from each eclipse by means of the tune 

 given in the ephemeris. 



In noting each observation, the state of the weather is attended to, 



