Who was the first scientist to get his picture on a postage stamp?

Who was the first scientist to get his picture on a postage stamp?
John James & Dr. Crawford W. Long. (both April 8, 1940)

The United States issued a 'Famous Americans Issue' in 1940. This series had 35 stamps with 7 groups of 5 stamps. One of the groups was 'AMERICAN SCIENTISTS': Here are all 5 of scientists: 1940, Apr. 8: John James (1 cent) (Scott Catalog # 874)1940, Apr. 8: Dr. Crawford W. Long (2 cent) (Scott Catalog # 875)1940, Apr. 17: Luther Burbank (3 cent) (Scott Catalog # 876)1940, Apr. 17: Dr. Walter Reed (5 cent) (Scott Catalog # 877)1940, Apr. 26: Jane Adams (10 cent) (Scott Catalog # 878)


Einstein.

Although Einstein did get his picture of a US postage stamp it wasn't until 1965.