A century of constants

Over 100 years ago, two men set out to provide a compilation of physical and chemical constants. After 16 editions, their work is now online and constantly being updated

Ever needed to check the melting and boiling points of some organic compounds or wondered how the acceleration due to gravity varies over the surface of the earth?

For a hundred years, scientist, engineers and chemists have relied for such information on one of that select group of books (including Bradshaw, Wisden and Mrs Beeton) which are better known by the names of their authors than by their cover titles. Tables of Physical and Chemical Constants was the idea of two young scientists, George Kaye and Thomas Laby, in J J Thomson’s research group in Cambridge. They had collected a wide range of data from various sources for the purposes of their research, and they noted in the Preface to the first edition that they had been impressed by the need for a set of up-to-date physical and chemical tables during their teaching and laboratory experience. Today the latest version of their brainchild can be accessed online at www.kayelaby.npl.co.uk.

Kaye left Cambridge in 1910 to take up a post at the National Physical Laboratory (NPL) and the Australian Laby left Cambridge in 1909 to become Professor of Physics in Wellington, New Zealand. They pursued their project at a distance, with Laby compiling the chemical data while Kaye was responsible for the values of physical constants and properties.

Published by Longmans, Green and Co in 1911, the first edition extended to 147 pages, consisting entirely of tables of figures covering a very wide range of topics.  In addition to mathematical tables, the eight sections were:

• General Physics, Astronomy, etc
• Heat
• Sound
• Light
• Electricity
• Magnetism
• Radioactivity and Gaseous Ionisation
• Chemistry.

Preparing and checking this work was a prodigious task, although the authors acknowledge the advice and assistance of a number of people in reading and correcting the proofs. Kaye had access to the results of determinations of constants at the NPL and they may have had assistance with the collection and tabulation of the data presented, but it appears that they undertook much of the work themselves.

The first edition begins with the atomic weights of the 81 elements known in 1910 and the following pages contain many (but not all) of the constants and quantities included in the latest edition. Thus, while we can find there the values of the thermal expansion coefficients of a wide range of solids, liquids and gases and the properties of more than 300 inorganic compounds, the solubilities are mostly expressed as ‘insoluble’, ‘soluble’ or ‘very soluble’. Of course some topics are no longer relevant and have been omitted from later editions. Thus the various experimental values of the velocity of light and measurements of radium levels in sea water are no longer reported, while the sparking potentials of air, Mrs Ayrton’s formula for electric arcs and Dr Common’s recipe for a silvering solution have long since disappeared.

Although the extent and scope of the book had grown steadily over the years, the original intention of Kaye and Laby that the information should be of value to specialists and generalists alike continued to be observed. Thus the 16^th edition, published in 1995, contained no fewer than 595 pages of data with completely new sections covering, for example medical ultrasonics, fibre optics, high temperature superconductivity and Raman spectroscopy. In addition, new chapters were added to provide introductions to laboratory safety and quality assurance, subjects which would be of interest to anyone working in a modern laboratory environment. In addition, the material on statistical methods for their treatment of experimental data was expanded into a separate chapter.

A very evident difference between the 1^st and 16^th editions is the much greater quantity of explanatory text in the later version. Kaye & Laby is not a text book, but the accessibility of the data to a wider readership is greatly enhanced by the introductory text in many sections. Thus the first chapter, Units and Fundamental Constants, begins with an introduction to the international system of units (SI) and the new section on superconductivity includes a half-page history of recent developments in the field. In many cases, the inclusion of footnotes and references allow the interested reader to find more detailed information.

By now the contents were under the supervision of a four-man Editorial Board, with sections provided by no less than 75 contributors, of whom more than half were present or past members of the staff of NPL, underlining NPL’s continuing investment in the ongoing work of Kaye & Laby and the provision of reliable scientific and engineering data to the wider laboratory community.

By the time of Kaye & Laby’s 90^th anniversary in 2001, the publishers had decided not to proceed with a 17^th edition and the idea of an online version was born. Rather than start again with a completely new website, the Editorial Board decided to put the 16^th edition online and with the support of the Institute of Physics the entire contents were digitised and compiled to a fully searchable website, hosted by NPL with a link from their website. Then followed a long process of checking and editing to ensure the accuracy of the contents and the suitability of the layout for online access. Particular attention was paid to the many equations, diagrams and graphs to ensure that they would appear correctly in different browsers. The result is a widely used online resource, visited by some 30,000 scientists, engineers and students a month.

One of the advantages of an online version is that individual sections can be edited or replaced without the need to publish a complete new edition and Kaye & Laby is now being kept up to date by regular revisions of outdated sections. These range from minor amendments to correct errors or clarify text to rewrites of whole sections where extensive new data are available or the original text has got out of date.

Providing a reference to a website in a publication is complicated by the risk of changes meaning that the information referenced may no longer be available to readers. In most cases, the best that authors can do is to specify the date on which the site was accessed, but the Kaye & Laby website includes a system of version numbering and archiving so that replaced or amended versions can be viewed at a later date.

Since the launch of Kaye & Laby Online, several sections have been updated, including the entries on barometry and thermal expansivity as well as the comprehensive catalogue of nuclides. In this centenary year, several major updates are in preparation. In particular, the table of fundamental constants in the first chapter is being edited to reflect the 2010 CODATA values which have just been published and the final three chapters on statistical methods, laboratory safety and quality assurance are all being rewritten to reflect developments since the 16^th edition was published and to add links to other important sources of information.

Kaye & Laby Online provides a reliable, comprehensive source of data for scientists and engineers. It is constantly being revised and updated to reflect the availability of better data and the requirements of modern science. To try it, just go to www.kayelaby.npl.co.uk and look for the information you use by browsing the Table of Contents or using the internal search engine. If you don’t find what you need or in the unlikely case that you spot an error, we welcome feedback to help us to continue to improve Kaye & Laby for its second century.

Author Seton Bennett, Chairman of the Kaye & Laby Editorial Board