In the mid-1950s, Johns became interested in making art using mechanical implements. His approach brought the act of making the painting to the foreground in a manner quite different from the presumed spontaneity of his abstract expressionist forbearers. Although he did not abandon targets as a subject matter altogether, in works like Device Circle, 1959, the artist began to incorporate mechanical objects in his work, such as a large compass that he attached to the canvas and swung in either direction to scrape paint off the canvas to form circles. 

By 1959, Johns went further and incorporated mechanically functional objects in his work. He also altered the canvas' surface by stenciling numbers and names of colors on it in an effort to separate himself from the creative process but still allude to the component parts of a painting. 

The Thermometer's vertical interruption of the canvas in Johns' Thermometer is a reference to Barnett Newman's zip paintings, which Johns would have seen on display at French and Company's spring 1959 exhibition in New York. The show was notorious because Newman was criticized for being overtly masculine, and an exchange of letters between the artist and the critic Hubert Crehan ensued.

Newman had included the 'zip' or vertical line in his work since the 1940s. It was a means of breaking the color field and bisecting the picture plane, forcing viewers to confront the ambiguity before them and look beyond the work.  The notion of the zip works as both a unifying and a dividing element. In Thermometer, the actual object, encrusted between the panels, works in similar ways. Johns brilliantly uses it as both a divider and as a unifying element.