Samuel Pierpont Langley was born on August 22, 1834. He could have gone to Harvard but instead chose to become an apprentice under an architect and a civil engineer. Langley trained himself as a scientist. He built amateur telescopes and toured around Europe visiting the different observatories. For a time he was professor of physics and director of the Allegheny Observatory in Pittsburgh, Pennsylvania.

From the time that Langley was a child the Sun fascinated him. He said "I used to hold up my hands and wonder how the rays made them feel warm, and where the heat came from, and how." He became actively involved in Sun research after he went on an expedition to observe a solar eclipse. He felt is was the "grandest spectacle nature offers" so he decided to start studying the heavens and especially the Sun.

He drew detailed drawings of sunspots. But he didn't know what they did and that started his search for the solar constant; which is the average amount of solar energy available above the atmosphere at the Earth's average distance from the Sun. He first began using a photometer in his investigations but it wasn't accurate enough because it couldn't give him an absolute quantitative measure.

He established the Smithsonian Astrophysical Observatory as a center for studies of "the new astronomy." He was personally interested in the Sun and the relationship between the Sun and the Earth.

In 1878 he developed an instrument he called his "ray measurer" or bolometer. Basically it was two thin platinum strips that were equal in dimension and electrical resistance. The strips were painted black and absorbed 97% of the solar radiation that fell on them. He connected a storage battery to them but when both strips were exposed to the same conditions no current would flow between them.

To work the bolometer and take a reading he would cover one of the strips and leave one exposed to the sunlight. When the uncovered strip became warmer its resistance increased and currents flowed which could be measured by the galvanometer. This made it possible to detect even minute temperature changes. Langley said that the effect was like putting your finger on the throttle of a steam engine.

He was doing this work in Pittsburgh, Pennsylvania and at the time there was a lot of smog from the industries in town. He thought the smog might be interfering with his work so he moved it to Mt. Whitney California. There the weather was so clear he was able to take more accurate readings. These readings which were 3.0 calories per centimeter per minute were the accepted number for the solar constant until twenty years later when his assistant, Charles Abbot, who later followed him at the Smithsonian corrected the number to 2.1 calories.

The Smithsonian Institution Annual Report of 1900 states, "Langley went down the spectrum, noting evidence of visible heat die out on the scale of the instrument until he came to the apparent end...beyond which the most prolonged research had shown nothing...By some happy thought, he pushed the indications of this delicate instrument into the region still beyond. In the still air of this lofty region, the sunbeams passed unimpeded to the mists of the lower earth, and the curve of heat, which had fallen to nothing, began to rise again. There was something there. For he found, suddenly and unexpectedly, a new spectrum of great extent, wholly unknown to science and whose presence was revealed by the new instrument, the bolometer."

From this research years ago the SAO now plans to have ready in 1998 an array of six submillimeter-wave radio telescopes that can make high resolution observations in the electromagnetic spectrum from Earth. This will open up a whole new ability to study the universe. It is a further advancement of the bolometer invented by Langley.

Samuel Langley died in 1906 after having a series of strokes. Solar research was just starting to show some real advancements in part helped by his research.