Excerpt from Industrial Electrical Measuring Instruments The illustrations are, in almost every case, diagrams showing working principles rather than views of the actual apparatus. Most engineers are already familiar with the outside appear ance of the instruments, so that external views are unnecessary, and photographs of working parts nearly always accentuate unimportant details to the exclusion of essential features. Wherever possible, diagrams and curves have been given in preference to formulae. Mathematicians will doubtless deplore the almost entire absence of mathematics, but, writing as an engineer, for engineers, the author is strongly of opinion that higher mathematics would be quite out of place. He believes that the only way to get a thorough insight into any phenomenon is to obtain a clear mental picture of what is taking place, and that, except to the mind of the trained mathematician, a mathematical solution too often fails to bridge over that wide gulf, which separates the abstract from the concrete