TOL. XIX.] PHILOSOPHICAL TRANSACTIONS. Q 



the angle, which is not six minutes in the first five days: nor need you inquire 

 the height or distance of your building, provided it be very great, so as to make 

 the spaces you measure large and fair. But it is convenient that the plane on 

 which you take the shade be not far from perpendicular to the sun, at least not 

 very oblique, and that the wall which casts the shade be straight and smooth at 

 top, and its direction nearly east and west, for reasons that will be well under- 

 stood by a reader skilful in the doctrine of the sphere. And it will be requisite 

 to take the extreme greatest or least deviation of the shadow of the wall, be- 

 cause the shade continues for a good while at a stand, without alteration, which 

 will give the observer leisure to be assured of what he does, and not to be sur- 

 prised by the quick transient motion of the shade of a single point at such a 

 distance. The principal objection is, that the penumbra, or partile shade of 

 the sun, is, in its extremes, very difficult to distinguish from the true shade, 

 which will render this observation hard to determine nicely. But if tlie sun be 

 transmitted through a telescope, after the manner used to take his species in a 

 solar eclipse, and the upper half of the object-glass be cut off by a paper pasted 

 thereon, and the exact upper limb of the sun be seen just emerging out of, or 

 rather continging the species of the wall, the position of ihe telescope being 

 regulated by a fine hair extended in the focus of the eye-glass, I am assured 

 that the limit of the shade may be obtained to the utmost exactness : and of 

 this I design to give a specimen by an observation to be iDade in June next, by 

 the help of the high wall of St. Paul's church, London, of which some follow- 

 ing Transaction may give an account. In the mean time what I have premised 

 may suffice to set others at work, where such or higher buildings are to be met 

 with. I shall only advertise, that the winter tropic, by this method, may be 

 more certainly obtained than the summer's, by reason that the same gnomon 

 afl^ords a much larger radius for this kind of observation. 



On the probable Cniises of the Pain in Rheumatisms ; and on the Cure of a total 

 Suppression of Urine, not caused by a Stone, by the use of yields. By Dr. 

 Edward Baynard, Fellow of the Col!, of Physicians. N" 215, p. \Q. 



This ingenious physician was always of opinion, that the pains in a rheuma- 

 tism were not caused by any saline or acid particles in the blood, &c. but rather 

 by its clamminess and density distending the channels through which it passes, 

 which distension produces those sharp and pungent pains which rheumatic per- 

 sons so generally complain of; for although the proper coats of the veins and 

 arteries seem to be insensible in themselves, yet those thin membranes which 

 beset them are of most exquisite sense, and full of lymphaeducts, which being 

 dilated and stietched, cause an inflammatory symptomatic fever, with continual 



VOL. IV. C 



