1872.] Heat. 123 
scope. The paper is accompanied with a plate containing twenty-two figures, 
drawn to scale, of the spectra of various coloured fluids, &c., compared with 
the lines of the solar sperum. 
Microscopists who are in the habit of making drawings with the aid of a 
tuled disc in the eye-piece,* will find the ‘‘seétional paper’? of Messrs. Letts 
convenient for recording theirobservations. This paper is ruled in squares of 
twelve different sizes, varying from ,}, inchto rinch. The lines are of a very 
pale-grey colour, so as to ‘be just visible, and scarcely interfere with the 
finished drawing, while they are sufficiently plain to guide the artist in 
copying from the ruled field of the microscope. 
A simple and efficient erector, for use with the compound microscope in 
dissection and other manipulations, has been contrived by Mr. E. Richards, 
F.R.M.S. It consists of a glass mirror platinised on the front surface placed 
over the eye-piece at an angle of 45°. The microscope is used in a vertical 
position, which allows vessels of fluid to be placed on the stage, while the 
observer looks forward at the reflected image. The reflection being from the 
front surface, the confusion occasioned by the double image of an ordinary 
mirror is avoided; the platinum surface retains its brilliancy for a longer period 
than one of silver, and the definition is extremely perfec. 
HEAT. 
Captain J. Ericsson has constructed an apparatus for measuring the radiant 
intensity transmitted by flames, to endeavour to prove that the radiant power 
of flames is not less than that of incandescent solid substances. The measure- 
ment of the radiant heat transmitted by flames is of great importance, as it 
furnishes a means of measuring with precision temperatures which cannot be 
ascertained by direct conta&. The construction of the apparatus is based 
upon the law that the intensities of circular radiators of different size, im- 
parting equal temperature at equal distance from the radiating surface, are 
inversely as the squares of the sines of half of the subtended angles, that is, 
the angles formed by the axes of the circular radiant surface and the heat rays 
projected from the circumference to the substance receiving the radiant heat, 
in the prolongation of the axes. It is thus possible to determine the 
temperature of a circular radiator without knowing its size and distance. A 
perforated diaphragm of polished silver is so arranged before a thermometer 
that the circumference of the perforation may form a known angle with the 
centre of the bulb of the thermometer. The metal cone containing the 
thermometer and diaphragm is surrounded with a water-jacket. Suppose 
the thermometer to indicate 282°, and the temperature of the surrounding 
water to be 73°, then according to the law laid down, if the angle subtended by 
the centre line of the conical vessel and lines drawn from the circumference 
ofthe flame-disc to the bulb of the thermometer be 16° 8’, we know that its 
temperature must be 12°gI times greater than that of the flame, or 2698° F. 
(282 — 73 = 209; 209 X I2‘°gI = 2698). Captain Ericsson promises a full 
extension of the application. 
A simple apparatus for the observance of some beautiful phenomena con- 
need with the vibrations of flames, &c., can be constructed as follows:—A 
disk of white cardboard, with apertures oblong in radial diredtion, is set ona 
spindle, so as to be rotated at any requisite speed. To examine, for instance, 
the flame of a gas light (in a glass tube, to prevent disturbance by air currents), 
place the disk in front of the light, so that the eye can see the light through 
each slit as it comes to a vertical position. If the speed of the disk’s 
rotation is such that the interval of time between two slits passing the eye is 
just equal to the period of a vibration of the flame, the flame appears to be 
motionless; but if the velocity be reduced, the flame is seen to go slowly 
through its changes of form. If the interval be equal to, or one-half of, or 
one-third of the period of the vibration of the light, the illusory appearance 
of adisk having as many, or twice, or three times the number of slits really in 
* Chemical News, vol. xxi., p. 30. 
