100 YEARS AGO

Symbol for Partial Differentiation. “The insufficiency of this notation is not forgotten, however, although its advantages over the different devices of Euler and Lagrange are recognised...”. I am glad to think that a pure mathematician sees the difficulty met with by users of mathematics. I wish that men who write to me privately would publish their remarks. One correspondent says: “I think 'the mathematicians' made a rather stupid blunder when they introduced ∂ for partial differentiation. This way: nearly all differential coefficients are partial; even a complete one (assumed complete) may become partial by extension of the field of operation. So an old investigation of Kelvin's, for example, using d throughout, is, by 'the mathematicians', replaced by the same using ∂ throughout, except one or two here and there! What is the use? It gives a lot of trouble and as the printers haven't always ∂'s, or proper sized ∂'s, it makes bad work. It should have been ∂ itself that was introduced for the exceptional use, thus making next to no alteration in the classical investigations.” These are indeed my own views, but as my pupils go forward to University examinations I advise them to adopt the fashion which is likely to please the examiners.

From Nature 17 July 1902.

50 YEARS AGO

Messrs. Blundell Rules, Ltd., Chaul End Lane, Luton, Beds, have issued a small handbook of 22 pages (price 6d.) describing their range of slide rules, and giving examples of the uses of the various patterns. Thus, in addition to the usual rules in various styles graduated for simple mathematical operations, there are others with log–log scales, commercial calculators, electricians' scales with appropriate quantities, and a timber calculator. Most of these scales are made entirely of a white plastic material, based on vinyl chloride–vinylidene chloride copolymers, with a 'satin' finish. It is claimed to be resistant to water, most chemicals and fungi. It is strong, and the scales are sharp and clear; in some patterns the tension of the slide can be adjusted. Model A.G.1 (£1 13s.), a simple general-purpose rule, has the usual A, B, C, D scales, and also scales for reciprocals, cubes and mantissæ; additional red lines on the cursor provide for finding areas of circles of given diameter.

From Nature 19 July 1952.