164 ANNUAL OF SCIENTIFIC DISCOVERT. 



ON SOME Ari'ARATUS FOR EXHIBITING OPTICAL ILLUSIONS 

 OF SPECTRAL PHENOMENA. 



Mr. H. Dircks, in a paper before the British Association on the above sub- 

 ject, after quoting some passages in Sir David Brewster's "Natural Magic," 

 in which the author had intimated that reflection by concave specula must 

 form the basis of all spectral illusions by reflection, and pointing out the 

 inconvenience of using these for producing images of living and moving 

 persons, in consequence of their inverting objects, stated that he had con- 

 trived a means by which living actors, some the real persons, others the 

 images of persons concealed from the direct view of the spectators, might be 

 formed by a large plate of glass dividing the room in which the exhibition 

 was made; the spectators being in a darkened portion above, but at one side 

 of the glass plate, while the living persons on the other side of it could be 

 seen quite clearly through the glass; and the images of other persons walk- 

 ing about in the room under them, seen by reflection, would appear in the 

 same place as the living persons seen directly, and could be thus made to 

 appear to perform most amusing spectral feats, such as passing through 

 walls, into and coming out of the living actors, and so on. 



NEW AND GIGANTIC TELESCOPE. 



Mr. Lassell, the eminent English astronomer, has been for some time 

 engaged upon the construction of a new and gigantic reflecting telescope. 

 The diameter of the mirror (not yet worked) is to be four feet, the same size as 

 Sir William Herschel's largest mirrors. Its weight is a ton and a half. The 

 tube is a skeleton. The mounting is equatorial, similar in its general form 

 to that which Mr. Lassell has used with smaller telescopes. A part of the 

 apparatus, of which the plan is perfectly novel, is the observing-box. It is 

 something like a very tall sentry-box, between thirty and forty feet high, 

 in which slides upwards and downwards a cage like the teagle of a cotton- 

 mill; in this cage the observer is stationed. The tall box stands upon a 

 ring-turn-table which surrounds the telescope's polar axis. The ring appears 

 to have a motion in azimuth, and the tall box has a radial motion on the 

 ring : and the combination of these two motions with vertical motion of the 

 teagle, gives command of the telescope's mouth in all positions. The tall 

 box is so arranged that, when the telescope is turned to a proper azimuth, 

 and is depressed to a nearly horizontal position, the tall box, turning upon a 

 hinge at its base, can be lowered over the telescope tube to protect it from 

 the weather. In addition to the particular motions described, the mounting 

 for the observer was hinged, so as to cover the telescope; and it also turned 

 upon an axis, so as to present the observer in the more favorable position 

 with regard to the eye-piece. 



ON THE INFLUENCE OF TEMPERATURE UPON PHOSPHORESCENCE. 



E. Becquerel has found that the color of the light emitted by phosphores- 

 cent bodies depends upon the temperature. Thus, sulphid of strontium, 

 obtained by the action of sulphur upon caustic strontia at 700 C. or 800 C., 

 is luminous with a violet light at ordinary temperatures, but changes its 

 tints when the temperature varies, and returns again to its original tint 

 when the original temperature is restored. In the case of sulphid of stron- 



