From the Editor

Perhaps it is appropriate in an issue featuring Optical En­gineering to discuss terminology: symbols, units, and nomencla­ture. In the May issue of this journal, Prof. Ingelstam has already discussed some aspects of the interplay between sci­entists and engineers. All of us who went to colleges which trained engineers remember the jocular distinctions between physicists and engineers; such as the engineer knows how but he doesn't know why and vice versa for the physicist. This philosophical distinction is also reflected in their attitudes toward terminology. In pondering a problem the physicist supposedly reasons his way to the solution. The effect is proportional to the fourth power of the temperature, say, or inversely proportional to the area. Being interested chiefly in dimensions he neglects the constants of proportionality and therefore tends to be indifferent about units. I t is precisely this indifference that makes him more willing to change his symbols and units and accept new definitions.

The engineer in general has much stronger feelings about terminology. When pondering a question he reaches for a hand­book to seek an analogous problem he has solved before, and he desires a numerical answer. I t is disconcerting, when trained to think in terms of Btu or foot-pounds, to find quantities ex­pressed in joules or kilowatt hours. The engineer relies chiefly on his memory rather than his reason, and there is something sacred to him about the way things were first learned. Gener­alizations such as the above are exceedingly dangerous and oversimplified; we all know engineers with poor memories as well as unreasoning physicists, but fortunately few of these are in optics.

When this journal began to take shape, long before the first issue appeared, we were asked by Deane Judd, the Editor of J. Opt. Soc. Am., what were our opinions concerning terminology. At that time we indicated we would go slow in formulating ed­itorial policies on terminology until we had a better feeling for the problem. As we saw it, we were attempting to lure into Applied Optics authors from many other disciplines on the fringes of conventional optics (such as electronics, solid-state physics, and space physics); to impose a common terminology on them might prove more difficult than on the J. Opt. Soc. Am. audience. So we were initially disposed to defer such matters as uniform terminology until a year or so had gone by and we had a better feeling for what changes might be required. However, as the papers came in for the first issue on optical pumping, our editorial sensitivity was deeply disturbed by statements such as "We used a 5-in. ruby rod and it made a 2-cm spot on the wall";

420 APPLIED OPTICS / Vol. 1, No. 4 / July 1962

"The spot was 5 mm in diameter and was imaged on the spec­trometer slit, which was ¼ in. long." This mixing of units demonstrates the hybrid nature of optical engineering: the physical properties of the radiation are expressed in metric units, and the engineering dimensions of the apparatus are expressed in "homely" units. (Your Editor has himself sinned in this manner; he once wrote a paper on atmospheric transmission expressing the water vapor concentration as "precipitable cm H2O per 1000 yards.")

We thereupon decided to see if we could not use the metric system throughout Applied Optics. By and large the authors consented quite readily to the proposed changes. When we inserted into the "Information for Contributors" a request that "in general, the metric system of units is preferred," we were somewhat embarrassed to see that the very next sentence was "Manuscripts should be submitted on 81/2 by 11 inch paper!" We are aware that there is nothing magical in the metric system— a distance is just as far in feet as it is in meters—but surely our communication with each other is improved when we use a common nomenclature. The metric system is slowly but surely winning general acceptance: for example, it was recently adopted by India and China, and even Great Britain is considering decimal currency and has adopted Celsius temperature.

Let us consider some more specific matters of terminology: In the past year, Dr. Judd has devoted two or three Editorials in J. Opt. Soc. Am. to optical terminology. In his April 1962 issue there is a detailed report on the SUN (symbols, units, and nomenclature) Committee of IUPAP and IUPAC, and the IAU is also participating in this effort to draw up a common list of preferred units, symbols, and definitions. This was discussed a t the March meetings of the J. Opt. Soc. Am. Associate Editors and the Applied Optics Editors and Reporters. Both journals decided to adopt these recommendations after they are approved by the AIP Publications Board. Some of these changes will begin in this issue (for example, Angstrom becomes Angstrom again). There will be a report on some of the proposed changes in the June Physics Today, and as soon as a revised AIP Style Manual is issued we shall expect authors to conform. We shall devote fu­ture columns to a discussion of the proposed changes in optics terminology, and we invite your comments. Some of the recom­mendations will probably excite controversy: for example, the recommended prefix for 1 0 - 9 is nano- and 109 is giga-. The old familiar mμ for millimicrons might give way to nm for nanometers (as used now by the Royal Society), and kMc for kilomegacycles becomes Gc, gigacycles. The recommended nomenclature for photometry is new to most of us.

The publications of the Optical Society represent a powerful segment of the optics literature, and if we adopt this proposed terminology we can make a real contribution to the clarity and precision of our scientific literature.

J. N. HOWARD