1868. | Physics ‘ 587 
flame-colouring salt. This plan in effect is suggested in Sir David — 
Brewster’s natural magic; but as the Bunsen burner was not then 
known, a less simple arrangement is described to perform the same 
office. The drawbacks to this arrangement are: the trouble of ad- 
justing the cotton wicks, the delay in changing to produce a new 
colour, and the brief duration and, to a certain extent, irregular 
amount of the effect. After lighting, the burners increase their 
effect to a certain point, and then soon rapidly diminish in the in- 
tensity of their light. When a large number of burners are to be 
used these difficulties become serious, and Professor Morton has 
therefore devised the following arrangement, which has proved, on 
trial, thoroughly efficient :—The burners to be used, varying in 
number from 5 to 30, in different experiments, are enclosed below 
in a box with a single large entrance, opposite to which is placed 
an atomiser, operated either by steam or compressed air. A spray 
of the colouring solution is thus mixed with the air supplying the 
burners, and their flames are thus tinged with the greatest ease, 
certainty, and intensity of effect, the whole action being entirely 
under control, and capable of being maintained indefinitely, while 
the change from one colour to another is effected by simply trans- 
ferring the tube of the atomiser from one solution to another. 
For experiments demanding diffused light this apparatus is most 
satisfactory. The author says that five large Bunsen burners, thus 
arranged, light up the lecture room of the Franklin Institute, which 
seats about 350 persons. 
In certain experiments, however, it is necessary to have mono- 
chromatic light of great intensity and concentration. This can be 
furnished in the case of yellow light, to a certain extent, by substi- 
tuting in the gas microscope or polariscope a soda-glass rod for the 
ordinary lime cylinder, and so adjusting its position that the rays 
from the heated glass should be cut off from the lenses, and only 
the light of the yellow flame should reach them. We can thus 
show, upon a screen 5 feet in diameter, the greatly increased num- 
ber of rmgs developed by a section of Iceland spar in monochro- 
matic light. With the spectroscope we can also project the sodium 
line on the screen so as to be well seen by an audience of 500 persons. 
By afterwards producing the absorption band due to the vapour of 
the substance, with the aid of asmall Bunsen burner and iron spoon 
with sodium, and again showing the absorption-bands of nitric 
peroxide and of cochineal, the characteristic phenomena of spectrum 
analysis may be sufficiently illustrated, without the trouble and 
expense of the electric light. 
A novel arrangement of stereoscope and slide has been brought 
out by Messrs. Warner and Murray, in which the inventors have 
taken advantage of an important feature in optics hitherto over- 
looked by all makers of the stereoscope, vz. that while the size of 
