The Joly meldometer was created to determine the melting point of minerals. W.E. Wilson, an astronomer and author, stated in 1900 that the Joly meldometer consisted of a ‘a strip of platinum on which minute fragments of any mineral can be placed, while any alteration in its length can be determined by means of a micrometer screw which touches a lever connected with one end of the strip. The strip can be heated by an electric current, and is calibrated by observing the micrometer readings corresponding to the temperatures at which some substances of known melting-points melt’i . One reason why the Joly meldometer was seen as a successful addition to science was the small amount of any substance that it required for testing. Only a minute sample was needed for the instrument to work and so a tiny part could be taken from a delicate item without destroying itii .
The instrument was originally manufactured by the Irish company Yeates & Son of Dublin. The Yeates family business was established in the early 1790’s and is thought to have operated until approximately 1922iii . Their business slogan was recorded as ‘Instrument makers to the University’, a slogan which proudly exhibited their relationship with Trinity College, Dublin. The company was located directly opposite Trinity College, the place where the Joly meldometer was created. Working in such close proximity must have assisted this business relationship.
The inventor of this meldometer was Irishman John Joly. Joly was born in 1857 at the Church of Ireland Rectory, Hollywood House. His education led him to Trinity College Dublin where, by 1891, he had obtained a Bachelor of Engineering degree as well as a Doctorate of Science. The entirety of his working life appears to have taken place at Trinity College although he is known to have travelled in order to consult with other scientists such as the world renowned Sir Ernest Rutherford.
The Joly meldometer was used for a variety of different purposes, with scientists often adapting the instrument to suit their own needs. For instance, the previously mentioned astronomer W.E. Wilson adapted the meldometer to assist him in measuring the radiation of the suniv . Joly used his device in an attempt to ascertain the age of the earth. In 1913, along with Sir Rutherford, Joly came to the conclusion that the earth was approximately 400 million years old. They did this by analysing the decay of radioactivity in minerals. According to our present knowledge of the earth this was a much more accurate date than the dates Joly had previously derived. He had first thought that the earth was 97 million years old due to the volume of sodium in the oceans. Joly’s second analysis of the topic had resulted in the age of 80 million years. This figure was based on the accumulation of sediment.
Apart from designing his meldometer, Joly is also remembered for his work with colour photography. In 1894 Joly discovered a method for creating colour photographs from a single platev . He also studied the use of radiation as a treatment for cancer and persuaded the Royal Dublin Society to establish the Radium Institute to assist hospitals. In 1933 Joly passed away at the age of seventy-six.