VOL. LXIII.J PHILOSOPHICAL TRANSACTIONS. 3Qg 



place, will be found to be widely different, if no correction be applied for the 

 error of the instrument. 



June, zenith distance —27° 59' 29-6" Dec. zenith distance 74^° 56' 57.8" 



Latitude of Greenwich 51 28 38 -51 28 38 



23 29 8.* 23 28 19.8 



But if the observations be corrected by the error of the instrument, the two 

 results will be found, to agree together as nearly as can be expected. 



Thus, 27° 59' '29.6" 74° 56" 57.8" Or, if the obliquity be required inde- 



— 27 59 43 74 57 33.6 pendent of a knowledge of the latitude 



51 28 38 —51 28 38 of the place, it will be found to be = 



Obliquity 23 28 55 23 .8 55.6 23° -28' 55".3. Thus, 



December 74° 57' 33.6" By comparing the observations at the sum- 



I)Xrence.!..!!..!.~46 57 50.6 mer solstices of 177 1 and 177'2, with those at 

 Mean obliquity 1690, the winter solstice of 1771, it appears that the 



i ditierence 23 28 55.3 uv -^ u .. ..u u • • r 



' mean obliquity was, about the beginning of 



the year 17 72, = 23° 28' Q".4 and 23° 28' 8*. Mr. H. supposes therefore the 

 mean obliquity to be 23° 28' 8" at the beginning of the present year; and con- 

 sequently the obliquity has diminished, by his observations, 47" in 81 years, 

 since Mr. Flamsteed's time, or at the rate of 58* in 100 years, a quantity which 

 will be found nearly at a mean of the computations framed by Mr. Euler and 

 Mr. de la Lande, on the principles of attraction. 



^f^. New Observations on P'egetation. By Mr. Mustel of the Acad, of Sciences 

 at Rouen. Translated from the French, p. I26. 



Many celebrated writers, induced by the analogy which they observed be- 

 tween the vegetable and animal kingdoms, have admitted the circulation of the 

 sap in the one, in a similar manner to the circulation of the blood in the other. 

 This important point of vegetable economy produced a diversity of opinions, and 

 has not yet been sufficiently cleared up. Dr. Hales, in his Vegetable Statics, 

 does not seem to embrace the system of the circulation of the sap; nor does he 

 prove the contrary.* 



Mr. Du-Hamel, in his Physiology of Trees, contents himself with relating 

 what has been said for or against this opinion ; but though he sufficiently hints 



* line prouve pas contre. This certainly is a mistake. Dr. Hales, in the -!th chapter of his Phy- 

 sical Statics, not only declares openly against the doctrine of the circulation of the sap, and overturns 

 the arguments alleged in favour of this opinion ; but he produces several new experiments, which 

 prove directly the impossibility of such a circulation. (See p. 144, &c.) His reasons have been 

 thought so convincing, that the system of the circulation in plants has bieen ever since exploded in 

 England ; and that they have had a similar effect abroad, appears from the following quotation from a 

 book of the ingenious Mr. Bonnet, f. k. s. of (Jeneva, entitled Recherches sur I'Usage des Fetiille.'s, 

 printed in 1754, p. '26^. ' Pour moi, persuade dela faussete de cette opinion (que la seve circuloit 

 comme le sang) par les experiences de M. Hales (ch. 4) &c.' M. M. — Orig. 



