aJaplcl to the rapid variation of density in the lens, which must, 

 therefore, be presumed to have some distinct mechanical utility^ 



2. The effort to view near objects is accompanied in most, it not 

 all persons, by a sensible muscular effort. 



3 This theory is free from the various conclusive objections 

 urged by Dr Young against all explanations which do "«* ^urn upon 

 a change of figure of the lens ; and it is also free from the difficul- 

 ties to the admission of Dr Young's tlieory,-the muscularity of the 



lens itself. . . . . 



4 When the lens is reproduced, after the operation for cataract, 

 the power of adjustment is greatly diminished or wholly lost, since 

 the variable elasticity will be wanting. 



5 The diminution of the adjusting power of the eye m old age is 

 explained by the increased rigidity of the lens, and consequent in- 



compressibility. . ^ .u * 



6 The crystalline lens polarizes light in a manner similar to that 

 exerted by glass and other uncrystallized substances in a state ot 

 constraint, That is. possessing unequal elasticity m different direc 



tions. 



2. Notice of an Ancient Beach near Stirling. 

 By Charles Maclaren, Esq. 

 This beach presents the appearance of a terrace, extending along 

 the north side of the Carse of Stirling, from the foot of Abbey 

 Craicr westward to Lecropt Church, and beyond it. Its length is 

 abou°t two miles; its breadth, at Lecropt Church, is about 200 feet, 

 at Airthrey Mineral Well 900 feet, and at Airthrey Castle near 

 half a mile. Its upper surface is nearly a dead level in both direc 

 tions. except where breaches have been made in it, by streams or 

 other agents. The elevation of this surface above the Carse in 

 about 85 feet, and above the Forth at Stirling probably 110 teet. 

 Rock is seen under the terrace at the village of Causeyhead, in the 

 bed of the River Allan, at the Bridge, and at the bottom of the 

 acclivity under Lecropt Church. Everywhere else the terrace seems 

 to consist of stratified sand and gravel, constituting a mass similar 

 in form and materials to our present beaches. Its preservation 

 may be attributed to the high rock of Abbey Craig, which protected 

 it from the action of the ancient tides when the sea stood at a con- 

 siderably higher level than it does at present. A remnant of a 

 similar beach is seen on the south side of the Carse, about a mile 

 southwest from StirUng. It consists of a hill of alluvial matter, a 



