188 S. P. Langley—The Actinie Balance. 
of the thermopile, as employed by Melloni and by Tyndall 
may almost be assimilated to a kind of handicraft, requiring 
long familiarity and the almost instinctive and unconscious 
adoption at every moment of precautions which would cer- 
tainly never suggest themselves to the untried observer. The 
this craft, had flattered himself that he might turn his famil- 
iarity with the thermopile to some useful account here, and 
might perhaps succeed from this cause, where others hat 
failed. He was obliged, however, to admit to himself that his 
success was so partial as to be very like failure. He succ 
with the thermopile in obtaining feeble indications of beat oP 
comparatively homogeneous rays in the diffraction reflectio? 
spectrum but these indications were all too feeble, and 0b 
tained at too great a cost of time and labor to make it possible 
to carry on our knowledge of the distribution of heat in the 
spectrum by means of the thermopile to any great extent be- 
yond the point where others had left it. 
