Capt. Lefroy on Observations of the Aurora Borealis. 4:57 



serve to extend considerably bur knowledge of the anatomy 

 and physiology of vision, nor is the subject by any means ex- 

 hausted. I have not time to investigate the matter fully, and 

 shall be happy to see fair and honourable competitors enter 

 the field. The verifications and variations of the experiments 

 by Dr. Lathrop were gratifying to me. 



This apparatus will illustrate many important points in 

 optics, and especially the physiological point of " single vision 

 by two eyes." It shows also that we do not see an object in 

 itself: but the mind contemplates an image on the retina, and 

 always associates an object of such a figure, attitude, distance 

 and colour, as will produce that image by rectilinear pencils 

 of light. If this image on the retina can be produced without 

 the object, as in the phanlascope, then there is a perfect optical 

 illusion, and an object is seen where it is not. Nay, more, 

 the mind does not contemplate a mere luminous image, but 

 that image produces an unknown physiological impression on 

 the brain. It follows, that if the nerves can, by disease or by 

 the force of imagination, take on this action, a palpable im- 

 pression is made without either object or picture. As this 

 would be most likely to occur when actual objects are excluded, 

 as in the night, we have an explanation of the scenery of 

 dreams, and the occasional "apparitions" to waking persons. 

 The murderer, too, has a picture stamped on the sensorium 

 by the sight of his victim, which ever wakes into vibration 

 when actual pictures are excluded by darkness. , 



LIX. Preliminary/ Report on the Observations of the Aurora 

 Borealis, made by the Non-commissioned Officers of the Royal 

 Artillery, at the various Guard-rooms in Canada. By 

 Captain Lefroy, 7?.^:/., F.Il.S. 



My dear Sir, Woolwich, May 18, 1850. 



IF you think the accompanying Report will be interesting 

 to the readers of the Philosophical Magazine, it is much 

 at your service. 



Yours truly, 

 R. Taylor, Esq, Edward Sabine, 



The system of observations on the aurora borealis, per- 

 mitted by Colonel Dynely, C.B., at my request, to be made 

 at all our regimental guard-rooms, under the sanction of the 

 officers in command, has now been continued for two years 

 in Canada, and for one year in Nova Scotia and Newfound- 



Phil. Mag. S. 3. Vol. 36. No. 245. Ju?ie 1850. 2 H 



