476 



NOTES AND QUEEIES. 



[No. 211. 



Luscious lays. Warton. 

 Sadly sweet. Potter. 

 Varied strains. Pope. 

 Thick-warbled notes. Milton. 



W. PiNKERTON. 



Ham. 



PHOTOGBAnilC CORKESPONDENCE. 



Photographic Exhibition. — We understand that 

 tlie Phototrr.apliic Society lias made arranjieuients 

 for an exhibition of photoj^raphs in the metropolis 

 during the months of January and February next. 

 The exhibition will not be confined to the works of 

 native photographers, but will comprise specimens 

 of the most eminent foreign artists, who have been 

 specially invited to contribute. From the advances 

 which have been made in this favourite art, even 

 since the recent exhibition in the rooms of tlic 

 Society of Arts, we may confidently anticipate 

 that the display on the present occasion will be 

 one of the highest interest. 



How much Light is obstructed by a Lens ? — Can 

 any of your scientific correspondents furnish me 

 with an approximation to the quantity of light 

 which is transmitted through an ordinary double 

 achromatic lens, say of Ross, Voightlander, or any 

 other celebrated maker ? Lux. 



Stereoscopic Angles. — I cannot agree to my 

 opponent's assumed amendment (?) (Vol. viii., 

 p. 419.) space, for the simple reason that it would 

 be virtually abandoning the whole of the points 

 in dispute between us ; when farther discussion, 

 and more mature consideration, only tend to con- 

 vince me more firmly of the correctness of the 

 propositions I have advocated, viz. : 



1st. That circumstances mmi and do arise in 

 Avhlch a better result is obtaineil in producing 

 stereographs, when the chord of the angle of 

 generation is more or less than 2^ inches. 



2nd. That the positions of the camera should 

 not be parallel but radial. 



I certainly thought that I had, as I intended, 

 expressed the fact that I treat the cameras ^??'e- 

 cisely as two eyes., and moreover I still contend 

 that they should be so treated ; my object being 

 to present to each eye exactly such a picture and 

 in such a direction as luoidd be j)resented under 

 certain circumstances. The plane of delineation 

 being a flat, instead of a curved surface, has 

 nothing whatever to do with this point, because 

 the curves of the retinas are not portions of one 

 curve having a common centre, but each having 

 its own centre in the axis of the pupil. That a 

 plane surface for receiving the image is not so 

 good as a spherical one would be, is not disputed ; 

 but this observation applies to photographs univer- 

 sally, and is only put up with as the lesser of two 

 evils. A plane surface necessarily contracts the 



field of view to such a space as could be cut out 

 of the periphery of a hollow sphere, the versed 

 sine of which bears but a small ratio to its chord. 



Tiiere is another misunderstanding into which 

 my opponent has fallen, viz. the part of the object 

 to be delineated, which should form the centre of 

 radiation, is not the most contiguous visible point, 

 but the most remote principal point of observation. 

 I perceive that this is the case from two Illustra- 

 tions he was kind enough to forward me, being 

 stereographs of a T square, placed with the points 

 of junction towards the observer, and the tail re- 

 ceding from him ; and in one case the angle of 

 the square is made the centre of radiation, and 

 while its distance from the camera is only six feet, 

 the points of delineation are no less than three 

 feet apart. 



To push an argument to the extreme to test Its 

 value, is quite right ; but this goes far beyond the 

 extreme, if I may be allowed such a very Hiber- 

 nian expression. 



No object, however minute, can be clearly seen 

 if brought nearer to the eyes than a certain point, 

 because It will be what is technically called out of 

 focus. It Is true that this point differs in different 

 individuals, but the average distance of healthy 

 vision Is 10 Inches. Now, adopting Mr. Merritt's 

 own standard of 2^ inches between the eyes. It is 

 clear that, supposing the central point had been 

 rightly selectetJ, the distance between the cameras 

 was only double what might have been taken as 

 an extreme distance. It is scarcely necessary to 

 suggest what a person devoid of taste (in which 

 category I am no doubt Included) might do in 

 producing monstrosities by adopting the radial 

 method, as such an one Is not very likely to pro- 

 duce good results at all. 



I now address myself to another accusation. It 

 Is quite true that I am uftacquainted with the 

 scholastic dogmas of perspective, but equally true 

 that I am familiar with the facts thereof, as any 

 one must be who has studied optical and geome- 

 trical science generally ; and while I concur In 

 the propositions as enunciated for a one-eyed pic- 

 ture, I by no means agree to the assumption that 

 the " vanishing points," In the two stereographs 

 taken radially with the necessary precautions, 

 " would be so far apart, that they could not in the 

 stereoscope flow into one ; " on the contrary, direct 

 experiment shows me, what reason also suggests, 

 that they do flow Into one as completely as in 

 nature when viewed by both eyes. 



I put the proposition thus, because I do not 

 hesitate to avow that In nature, as interpreted by 

 binocular vision, these points do not absolutely, 

 but only approximately, flow into one ; otherwise 

 one eye would be as effective as two. 



I have not the smallest objection to my views 

 being considered "false to art," as, alas! her fidelity 

 to nature Is by no means beyond suspicion. 



