1904-5.] Nriets R. FINSEN—HIs LIFE AND WorK. 117 
When the parts had been sufficiently treated, the raised edges became 
flat, the redness disappeared, the parts became natural in appearance, 
and if there was ulceration it healed over. Scars were quite insignificant. 
The effect of the treatment continued for some time after the treatment 
was stopped, sometimes for several months. 
The first apparatus used was one for concentrating sunlight, it con- 
sisted of a hollow plano-convex converging lens, 20 to 40 centimetres in 
diameter, filled with water colored blue by methylene blue or an ammonia- 
cal solution of sulphate of copper, to exclude most of the heat rays. Later, 
the coloring matter was omitted as excluding too many useful rays. Blue 
cut out most of the ultra-violet rays, while clear water absorbs the ultra- 
red rays largely, and it is chiefly the latter rays which cause the heat. 
Through this simple apparatus mounted on a forked stand, which could 
be raised or lowered, the rays of the sun were focussed upon the diseased 
area, the patients. sitting in chairs, or lying on tables out in the open air, 
Fic. 2—Diagram of Finsen’s Original Are Light Apparatus, showing large glass lenses and heat filter. 
But, as the sun’s rays were not always available, the voltaic are was 
utilized, the rays of which be'ng divergent, unlike the parallel rays of the 
sun, required a different contrivance somewhat like a telescope, consist- 
ing of two cylinders, each containing two plano-convex lenses. Two 
close together at the outer end of the outside tube, and having their 
plane surfaces towards the source of light, to cause the divergent rays to 
become parallel; the two other lenses so arranged as to make the parallel 
rays become convergent into a cone, which is allowed to fall on the part 
under treatment, but not at the focus but a little in front of it. Between 
the two latter lenses there was a layer of distilled water, and outside at 
the end next the patient a light filter of blue solution, which was later 
discarded. ‘The intensity of the arc light used varied from 35 to 50 am- 
peres. The apparatus was suspended from the ceiling of the room, and 
to economize the electric current, four tubes were placed about the arc- 
light at an angle of 45 degrees, so that four patients could be treated at 
the same time from one lamp. 
During 1897 Finsen made several improvements in his apparatus; 
