264 H. Draper—Oaxygen in the Sun. 
electric machine which can produce a current powerful enough 
to give, between carbon points, a light equal to 500 standard 
candles.  Whén'this machine is properly applied to the 17-inch 
induction coil; it will readily give 1,000 10-inch sparks per 
minute. ese, being condensed by fourteen Leyden jars, com- 
municate an intense incandescence to air, and light enough is 
produced to permit of the use of a narrow slit, and of a colli- 
mator and telescope of long focus. 
Since 1877, when the first publication of the discovery of 
oxygen in the Sun was made, still further improvements, es- 
pecially in the optical parts, have been completed, so that Iam 
now enabled to photograph the oxygen spectrum with four 
times the dispersion then employed. For the sake of clearness, 
it is best to give a brief description: Ist, of the electrical part; 
and 2nd, of the optical part. : 
he electrical part consists of the Gramme machine and its 
driving engine, the induction coil, the Leyden jars, and the 
terminal or spark compressor. An advantage the Gramme has 
over a battery is'in the uniformity of the current it gives when 
an uniform rate of rotation of its bobbin is kept up. Of course 
this implies the use of a prime mover that is well regulated. 
The petroleum engine of one and a half horse-power I have 
employed’ is convenient and safe and does this duty well. As 
to the Gramme itself, it is only needful to call attention to a 
modification of the interior connections. In one form the 
bobbin of wire which revolves between the magnets is double, 
so that the current produced may be divided into two. Under 
ordinary circumstances, where the machine is used to produce 
light, both sides of the bobbin send their currents through the 
electro-magnets. But if the whole current be sent through a 
quick-working break circuit into an induction coil, the electro- 
magnets do not become sufficiently magnetised to produce any 
appreciable effect. It is expedient, therefore, to arrange the 
connections so that one-half of the bobbin gives a continuous 
current through the electro-magnets and keeps up the intensity 
of the magnetic field, and then the current from the other half 
of the bobbin may be used for exterior work, whether contin: 
uous or interrup! 
nged to 
make and break the current passing into the primary circuit of 
