254 Mr. Shaw on the < Sense ' of Muscular Action, #c. 



may derive assistance from attending to the intimate connexion 

 which has been shown to exist between the retina and the muscles. 

 When it is observed that the state of activity of the optic nerve 

 draws along with it an activity of the muscles, and that both 

 these parts are equally engaged in the simplest act of percep- 

 tion, it is to be expected that the derangement of the one will 

 materially affect the other. But the nature of these actions of 

 the muscles of the eye cannot be properly understood, unless we 

 attend also to the involuntary motions of the eyeball ; by which the 

 eye, at the instant that the optic nerve falls into a state of repose, 

 becomes subject to the operation of a distinct class of muscles. 

 The consideration of these subjects, together with the study of 

 the complicated process by which an act of perception is com- 

 pleted, may perhaps throw some light upon the questions of 

 disordered vision, hallucinations, and some of the delusions of 

 the mind arising from false perceptions of the objects of sight. 

 For the principles on which these views of the nature of vision 

 are founded, I beg to refer my reader to the ' Essay on Single 

 Vision,' by Dr. Wells ; where the first indications will be 

 found of the knowledge of a ' muscular sense ;' to the posthu- 

 mous writings of Dr. Brown ; but more particularly to the 

 papers published by Sir Charles Bell, on the nerves which 

 supply muscles, and on the nerves and muscles of the orbit. 



ON THE INDURATION OF CHALK AND CHALK EARTH 

 UNDER WATER, AND THE APPLICATION OF THIS PRO- 

 PERTY IN HYDRAULIC ARCHITECTURE. 



By J. PENNISTON. 

 [In a letter to Dr. Fowler, of Salisbury.] 



Dear Sir, 



IN compliance with your wish, I will relate to you, in writing 

 the practical observations I have been enabled to make of 

 the properties which chalky substances have of consolidating 

 and hardening in the water. 



The first circumstance of any consequence that occurred 

 to me in this way was previous to the repair of Harnham 

 Bridge, which it was my professional duty to direct as Surveyor 

 for the county of Wilts. 



I was then induced, on the recommendation of the foreman 



