236 PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



different from the coagulable lymph, the coagulable part of the serum, the putres- 

 cent mucilage, and the red particles, which I believe are all the kinds it has hitherto 

 been supposed to contain. 



The microscopical observations of Mr. Hewson appear likewise to furnish a rea- 

 son, why both water, and a saturate solution of a neutral salt, can extract colour 

 from the red globules, though a mixture of those fluids be incapable of the same 

 effect. For water applied to the red globules, separates the exterior vesicles from 

 the red particles, which are therefore now open to the action of any solvent.* The 

 addition however of a small quantity of a neutral salt to the water, enables the 

 vesicles to preserve their shape, and to retain the inner spherules. -J- On the addi- 

 tion of a greater quantity of salt, the vesicles contract, and apply themselves closely 

 to the red particles within. J Thus far Mr. Hewson's observations extend. Let 

 it now be supposed that the vesicles contract still more, from a further addition 

 of salt to the water; the consequence must be, that as the internal particles are in- 

 compressible, the sides of the vesicles will be rent, and their contents exposed to 

 the action of the surrounding fluid. Both water and a strong solution of a 

 neutral salt may therefore destroy the organization of the vesicles, though in differ- 

 ent ways, and thus agree in bringing the red matter in contact with a solvent ; 

 while a mixture of those 2 fluids, namely, a dilute solution of a neutral salt, will, 

 by hardening the vesicles, increase the defence of the red matter against the 

 action of such substances as are capable of dissolving it. But all reasoning founded 

 on experiments with microscopes ought perhaps to be regarded as, in great measure, 

 conjectural. 



XX. An Account of the Trigonometrical Survey, carried on in 1795, 1796, by 

 Order of the Marquis Cornwallis, Master General of the Ordnance. By Col. 

 Edw. Williams, Capt. Wm. Mudge, and Mr. Isaac Dalby. Communicated by 

 the Duke of Richmond, F. R. S. p. 432. 



According to the resolution expressed in the account of the trigonometrical 

 survey, printed in the Phil. Trans, for the year 1795, we now communicate to the 

 public, through the same channel, a further account of its progress. On referring 

 to the above paper, it will be found that, for the prosecution of this undertaking, a 

 design was formed of proceeding to the westward, with a series of triangles, for the 

 survey of the coast. This intention has been carried into effect ; and as the small 

 theodolite, or circular instrument, announced in our former communication as then 

 in the hands of Mr. Ramsden, was finished early in the summer of 1795, we are 

 enabled to give a series of triangles extending, in conjunction with those before 

 given, from the Isle of Thanet, in Kent, to the Land's End. In the composition 

 of the following account, we have adhered to the plan adopted in the last, of giving 

 the angles of the great triangles, with their variations ; and we have, with as much 



* Hewson's Works, vol. iii. p. 17.— — f Ibid. p. 40. % Ibid. p. 31. — Orig. 



