VOL. LXXXVII.J PHILOSOPHICAL TRANSACTIONS. J? 



One of the principal tavern-keepers in London was rendered very uneasy by a 

 pain in the fore-arm, close to the elbow, which at times was very severe. On 

 examining the parts, the pain was evidently not in the joint, but appeared to arise 

 from an affection of the supinator brevis muscle, as the motion of that muscle 

 gave pain. This I stated to him, but told him I was at a loss to find out in what 

 way that part could have been injured ; this was readily cleared up, when he in- 

 formed me that the greatest pain he felt was in drawing claret corks, which he did 

 with a jerk or sudden motion of the arm, and it was immediately after an exertion 

 of this kind that he had first felt the complaint. It was clear from this account 

 that this particular muscle had been strained, and was rendered unfit to bear any 

 violent action. 



These cases will be sufficient to explain that a muscle, or set of muscles, may be 

 unable to perform those actions which require the greatest exertion, though capable 

 of performing all the others. If then we consider the disease which causes the 

 inability to see near objects as a strain on the muscles, and compare it with the 

 same disease in other muscles, there will be no difficulty in accounting for the 

 bad effects produced by every thing that irritates, or weakens the parts themselves, 

 or the general habit : it will follow, that such a mode of practice should be laid 

 aside, and those means adopted by which the parts can be soothed in their sensa- 

 tions, and quieted and strengthened in their actions, since in that way only the 

 muscular fibres can possibly recover their tone. 



Of double vision. — Many opinions have been advanced to account for the single 

 appearance of objects when seen by both eyes. Dr. Reid of Glasgow, who has 

 taken much pains on this subject, has treated it with much ingenuity and know- 

 ledge ; and the opinion he has advanced, of objects appearing single when the 

 impressions from the object are made on parts of the retina of the 2 eyes which 

 correspond with each other, and double whenever that is not the case, is very 

 strongly confirmed by the following observations on double vision. 



There are 2 circumstances under which double vision takes place : one where the 

 muscles of the eye do not correspond in their action^ and therefore the 2 eyes do 

 not bear equally on the object ; the other where some change has taken place in 

 the refracting media of one eye, which prevents the pencils of light from im- 

 pressing the corresponding parts of the retina of both eyes. Instances of double 

 vision produced by these 2 modes have fallen under my notice. It has been long 

 ascertained by experiments, that when the eyes are not turned equally towards an 

 object, it appears double, and the disease in the muscles which produces this effect 

 is the subject which I now mean to consider. It will at the same time be proper 

 to distinguish this kind of double vision from that which is produced by a change 

 in the refracting media of the eye ; and this will be best done by explaining the 

 nature of those changes in consequence of which it occurs. 



When one eye has had the crystalline lens extracted, the other remaining per- 

 fect, objects seen by both eyes will appear double. This is a fact which was no- 



