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John Rennie (1850-1917)
1917 Obituary 
JOHN RENNIE, born at Ayr in 1850, and educated at a Free Church school, began his training in large shipyards at Glasgow.
When 26 years of age he entered the University of Glasgow and gained the Thomson Experimental Scholarship in physics.
In 1881 he became secretary and private assistant to Sir William Thomson, and for nine years worked on the development of the Kelvin electrical measuring instruments, and helped with many of the researches which were being conducted. If ever a great man had a faithful disciple who felt it an honour to carry on part of the results of his master's life, with his ideals of scientific truth and scrupulous accuracy, here was one.
In 1890 he was appointed electrician of the Board of Trade Electrical Standards Laboratory, which seemed likely to become an establishment of some importance. But it met with so much official discouragement and restriction that he never took the place in the scientific and engineering world that was his due.
During the 27 years in which the Laboratory was under his charge he proved that the Kelvin balances and electrostatic voltmeters were not only worthy of the original requirements, but that they have been capable of those much higher degrees of precision which are necessary at the present day.
In the early days of the Board of Trade Electrical Standards Laboratory Mr. Rennie working under Major Cardew compared the various standards and sub-standards, and minutely investigated the instrumental errors, and kept records of the histories of the important apparatus. When, with the development of electrical engineering, three-phase working opened a branch of work which the Kelvin instruments did not directly cover, he kept himself well abreast of the principles of three-phase measurement.
When it became necessary to procure suitable wattmeters, he was very exacting in his requirements and expected more from the instruments than was easily provided. Perhaps the most important work of his life was expended on electric meters. The fact that notwithstanding the inadequacy of legislation with regard to meters so little trouble has been experienced, that such excellent meters are in use, and that so few are ever disputed, is the outcome of his incessant work on the subject.
With his unique knowledge of the construction of electric meters he was able to point out to those who submitted types for official approval defects which would show themselves after prolonged tests. This approval was coveted not only by British but by foreign makers, and so thorough were his criticisms that gradually nearly all the meters in use were of the approved types. He was a retiring man personally unknown to many engineers but well appreciated by those few who had to deal with him. He had high ideals in human affairs as well as in science. When some verification had been made with six-figure accuracy, he used to say, "The 'Old Man' would have liked that."
He died after a month's illness on the 19th February, 1917.
One of his sons was killed in action in the fourth month of the War, another is in the Royal Naval Division abroad, and the third has a commission in the Royal Naval Air Service. Mr. Rennie leaves a widow and two daughters.
He was elected a Member of the Institution in 1890.