Mr F. Marcet on the Action, of Poisons, fyc. 293 



When the same star is seen by indirect vision, it reappears 

 with a degree of brightness which it never assumes when seen 

 directly by the eye. When the eye is adjusted to the distinct 

 perception of an object placed in the axis of vision, an object 

 placed out of the axis cannot be seen with the same distinct- 

 ness, both from the pencils not being accurately converged 

 upon the retina, and from the expansion of the image, which, as 

 we have already described, accompanies indirect vision. A 

 luminous point, therefore, seen indirectly, swells into a disk, 

 and thus loses its sharpness, and acts upon a greater por- 

 tion of the retina.* In order to determine whether this ex- 

 pansion, and the image of the luminous point, was the cause 

 of its superior visibility, I turned my eye full upon a lumi- 

 nous point till it ceased to be visible, and then, re-adjusting 

 my eye, so as to swell the point into a circular disk by direct 

 vision, I invariably found that its visibility was instantly in- 

 creased. If this explanation of the phenomenon be the cor- 

 rect one, the practical astronomer may, with direct vision, ob- 

 tain a clearer view of minute and faint stars, either by putting 

 the telescope out of its focus, or by adjusting his eye to nearer 

 objects. 



Allerly, September 5th 1825. 



Art. XVI— On the Action of Poisons on the Vegetable King- 

 dom.f By Mr F. Marckt. 



Although the great work of M. Orfila contains a complete 

 and precise history of poisons, and of their action on the animal 

 economy, yet M. Marcet considered, that it would be desir- 

 able to make some experiments of the same kind on plants the 

 tissue, and some of the organs of which, have such a striking 

 analogy with those of animals. 



M. G. F. Jaeger, had previously published some interesting 



• The eve is not capable of observing correctly the colour* of lumi- 

 nous points seen indirectly A blue luminous point, for example, appears 

 nearly white. . 



+ This interesting paper, is a translation and abstract of a Memoir 

 which will appear in torn. HI- part i. of the Men, * fa .W. A ■ PA.y.. tf 

 rfllht. A'at. de Geneve. It was read on the 16th December 1881. 



