r 



VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 41 5 



been accurately observed at Greenwich or Paris, or at some place in Europe, 

 whose longitude from them is well known. But that failing us, I had re- 

 course to the period of the lunar motions, which is performed in 1 8 years and 

 10 or 11 days, after which the errors of our lunar computations return very 

 nearly the same; and I found among my own old observations, one that an- 

 swered well with that of the 4th of August, viz. Anno 1676, July 23, 13^ 

 1 1*" 35% at Oxford, I observed the moon to apply to the star in Medio Collo 

 Tauri, by Bayer marked a. The star at that time was distant from the southern 

 and nearest cusp of the moon by the micrometer 20' 32''', and at 13*^ 17™ 15^; 

 when it seemed to immerge on the bright limb of the moon, it was distant 

 from the northern cusp 23' 20 " ; but this less certain by reason of the hazy 

 air. The star at that time was in y 28° 56', with T 13' 20'^ north lat. by 

 which I found that our lunar tables, founded on Sir Isaac Newton's correct 

 theory of her motion, gave her place at that time only 2 minutes too slow; 

 which error being allowed on the 4th of August 1694, the result was, that 

 5^ Sg'" at Cape Bonne Esperance, was at London 4^ 53"^; whence the differ- 

 ence of longitude 164-°, is sufficiently near what we had before determined.* 1 



Jacohi Keill, M.D. De Firibus Cordis Epistola. N°36l, p. 995. 



A reply to Dr. Jurin's paper on the propulsive force of the heart ; a transla- 

 tion of which is omitted for the reasons before assigned at p. 375 of this volume. 



^n Account of some Experiments relating to the Specific Gravity of Human 

 Blood. By James Jurin, M. D. and F. R. S. N° 364, p. 1000. 



It is well known, from the observations of Mr. Leuwenhoeck and others, 

 that human blood consists of red globular particles, swimming in a pellucid 

 lympha, or serum. Which two different substances, though of unequal spe- 

 cific gravities, yet so long as they continue to circulate in the veins and 

 arteries, are prevented from separating by their motion and warmth. But 

 when the blood comes to stagnate and cool in a porringer, "^'le globular parti- 

 cles, uniting together by their attracive power, and sinking by their weight, 

 which is greater than that of the serum, form the coagulum, or crassamen- 

 tum, at the bottom, the serum swimming above it. 



This always is the case, when the crassamentum is at liberty to subside : 

 but it often happens that, either by its adhesion to the sides of the vessel, 

 or by the bubbles of air, which the blood gathers on falling into the porringer, 



* It is now known that the more accurate number is 1 8° 23'. 



