m the Invisible Prismatic Spectrum. 185 
Such a construction was applied to the prismatic energy 
curve of the Hilger prism. 
Fe for each vibration number to get the abscisse, and (observ- 
ing that since y now =4, = —~ =) to use the multiplying fac- 
er z obtain the height of the new ordinate in each instance. 
from which n 3 
; wa and c are indefinitely small, b and d are the ordinates of the pris- 
matic and normal energy curves, respectively, at a given wave-length, and ¢ is the 
ngle formed by the tangent to EF at their point of intersection. Hence, to 
. the height of the normal curve at a given wave-length, the corresponding ordinate 
of the prismatic curve must be multiplied by tan ¢. : 
4, 
F 
D 
A c - 
22 
: This Journal, for March, 1 
oSaamaaaa ordinate of the normal curve is through an error in he dra 
~ WD quite in its true position, nearly at A=0°55). 
& AM. Jour, So.—Tarep Senms, Vou. XXVII, No. 159—Mancu, 1594 
. 43 
i 
"a 1,0 : 4 : 
IV (where, however, the - 
883, Plates III and Le Se a 
