4 Sir Everard Home on the black -rete mucosum of 
the concentrated rays felt warm, but gave no pain, although 
applied for ten minutes. 
When the heat to a thermometer was 79 0 , that is at 15 
minutes past two o’clock (including the twelfth figure in the 
annexed drawing), the concentrated rays in four minutes 
gave pain ; in five minutes blistered the skin, and produced 
dots of coagulable lymph, which became vascular under the 
eye. 
When the heat to a thermometer was 82°, that is at half 
past two o’clock, (including the 13th figure of the drawing), 
the concentrated rays in three minutes gave pain; in four, 
the part was blistered, and the pain could not longer be 
endured. 
Experiment 6. 
September 8th, 1820, at eleven o’clock, the heat in the sun 
90°; the concentrated rays applied to my naked arm pro- 
duced a vesicle. This experiment was repeated when the heat 
was 84°, and in seven minutes a blister formed on the arm. 
Experiment 7. 
September 9th, eleven o’clock, the thermometer in the sun 
at 90°- The concentrated rays applied to a piece of black 
kerseymere cloth, made tight round my arm for 15 minutes, 
gave no real pain, and left no impression whatever on the 
skin, although the nap of the cloth had been destroyed. 
This experiment was repeated with white kerseymere, the 
heat at 86° ; in 15 minutes a blister was formed. 
Repeated with Irish linen, the thermomenter 86". In 15 
minutes a blister was formed, and coagulable lymph thrown 
out, which had become vascular. 
