The Barons Rayleigh and Corning UV Glass

The last post discussed early UV-VIS spectrophotometers. Those systems required phototubes with envelopes that pass UV. Corning’s ( Corex ultraviolet transmitting glass fit the bill and found application.

Apparently, there is another feature of Corex, although the author does not state exactly which material he studied:

Double Refracting Structure of Corex Glass

Nature, Volume 126, p. 845 (29 November 1930)

Some years ago I found that silica glass showed a doubly refracting structure (Proc. Roy. Soc., A, vol. 98, p. 284; 1920. Also Proc. Optical Convention, Part I, p. 41; 1926). This structure is quite distinct from any due to bad annealing, and seems kindred to the ‘liquid crystals’ of Lehmann. Nothing of the kind could be found in the ordinary glasses consisting of silica with metallic oxides.

I now find that the ultra-violet transmitting Corex glass of the Corning Co. shows a similar structure. This glass is said to consist in the main of calcium phosphate, though I have not seen an analysis. The subject evidently requires detailed examination, which I hope to make as opportunity allows.

(Robert John Strutt, 4th Baron) Rayleigh
Terling Place, Chelmsford,
Nov. 14.

This Lord Rayleigh is the eldest son of TheLord Rayleigh (John William Strutt, 3rd Baron Rayleigh). The unit, Rayleigh, is named in honor of #4, commonly known as Robin.

#3 established a laboratory at Terling Place, the family’s residence. #4 resigned his chair in physics at Imperial College after #3 died in 1919 and continued his research in the laboratory at Terling Place. Gentleman (or independent or citizen) scientists understand the benefits of WFH (working from home).

Unlike electronics, vintage optical datasheets are harder to find online. Here are some comments uncovered from a confidential US document that looked at materials and methods from 1920-1950 (G.L. Harvey, “A Survey of Ultraviolet Communication Systems,” NRL Report 6037, March 13, 1964):

“Corex D is useful for bulbs on sunlamps as it transmits the erythema or sun tanning wavelengths which are most effective at about 2967A while cutting out the less desirable germicidal mercury line at 2537A. The most effective wavelength for germicidal effectiveness is 2600A, dropping to very little bactericidal action at 3200A.”

Corex D appears to be Corning 970. Corex A (red-purple glass) appears to be Corning 986 or 986A (think black-light lamp). Clear Corex A appears to be Corning 980. But, this could be wrong. When material properties or some datasheets are found, they will be posted. It would be nice to see confirmation of #4 Lord Rayleigh’s observations of double refraction in Corex.

Corning Print Ad, 1938

For more information on the optical work of #4, see his son Charles R. Strutt’s article, “The Optics Papers of Robert John Strutt, Fourth Baron Rayleigh,” Applied Optics Vol. 3, No. 10, p. 1116-1119 (October 1964). Charles is the father of #6, John Gerald Strutt, The Lord Rayleigh.


Carrots and the First UV-VIS Spectrophotometer

World War II generated a lot of interesting propaganda and a lot of interesting hardware. In this post, we’ll see a mix.

From 1939-1945, Great Britain was dark at night as a result of wartime blackouts that were designed to make it difficult for the Germans. “Carrots provide a good remedy for blackout blindness, which afflicts many a Briton, on these wartime nights and have the additional merit of improving the complexion, the British have been told officially. The Ministry of Agriculture in London declares that carrots are the best source of Vitamin A, which is healthy for healthy eyes. They should be eaten raw, as cooking tends to destroy the vitamin. “If we included a sufficient quantity of carrots in our diet,” said the ministry, “we should overcome the early prevalent maladay of blackout blindness.” Carrots are termed the best vegetable for improving the complexion, by Gaylord Hanser, Hollywood beauty expert, according to the Ministry.” [1]

Food was scarce, but there were plenty of carrots and carrots were inexpensive. The British government wanted Britons to eat more carrots. They generated interesting recipes to help facilitate it…even carrot fudge.

Perhaps more hopefully, the British government wanted the Germans to think that the reason British fighters were succeeding against German aircraft at night was…..carrots. They did not want the Germans to know about its new airborne RADAR, which was responsible for thwarting the nighttime raids. It’s doubtful that the German bought the story.

But this note is not really about carrots. Leading up to World War II, the US military was confronted with a young male population that was suffering from a nutritional deficit caused by The Great Depression. There was a big push for more research into vitamins and nutrition. Vitamin A is important to good health and it received a lot of attention.

Before 1942, the standard procedure for measuring the concentration of Vitamin A in a food supplement/sample was:

  1. Feed the sample to rats for three or four weeks
  2. Measure the growth in the length of the rats’ tails
  3. Develop a model for tail bone growth as a function of Vitamin A concentration

Dr. Arnold O. Beckman had a better solution. He said, “In 1940, no one at National Technical Laboratories had any extensive experience in spectrophotometry. The fact was recognized, however, that the amplifier of the Beckman pH meter was well suited for use with vacuum-type phototubes. The company began a spectrophotometer development program in early 1940, and the responsibility for this program was assigned to H. H. Cary. Consulting assistance was sought from recognized optical experts, but World War II was under way and experts were hard to find. Roger Hayward, a professional architect and amateur scientist with some optic experience from his association with the Mount Wilson Observatory, provided a needed link to monochromator technology. His genius for quickly translating ideas into useful sketches was partially responsible for the extreme rapidity with which the DU spectrophotometer was developed. Douglas Marlow provided proficiency in mechanical design.

The Beckman DU at the time of product launch.

The first instrument designed was a glass Fery prism instrument, but its performance was not considered suitable. A quartz prism Littrow design with a tangent-bar drive followed and was designated the Model Β. Of the two quartz Model Β instruments produced, one was sold to the Chemistry Department of the University of California of Los Angeles in February 1941, and the other is in the company’s historical museum. This instrument utilized a tangent-bar mechanism which provided a substantially linear wavelength scale. Unfortunately, the scale was too compressed, particularly in the ultraviolet region, and was replaced by a Model C with its innovative scroll drive, which was used in all subsequent Beckman quartz prism monochromators. Of the three Model C instruments produced, California Institute of Technology, Vita Foods Co., and Riverside Experiment Station each purchased one. The Caltech instrument was later returned to the company for its museum.” [2]

After Beckman’s DU, the process for Vitamin A concentration measurements became:

  1. Dissolve the nutritional sample in water
  2. Place it in the DU and measure absorption

Rats were spared, researchers were spared the three weeks for tail growth, and the military improved the nutrition of warfighters. Yes, carrots were tested in a DU!

It’s important to note that visible and IR spectrophotometers were already present in the marketplace by the time of the DU’s introduction. However, Dr. Beckman realized that biological samples required UV sources and optical systems. The DU was the first commercial UV-VIS device. This was a very big deal.

I’m hunting for a DU to inspect and perhaps refurbish.

[1] “Carrots Remedy for Blindness,” The Daily Colonist, Victoria BC, FEB 9, 1941.

[2] Beckman, A.O., Gallaway, W. S., Kaye, W., and Ulrich, W. F. “History of Spectrophotometry at Beckman Instruments, Inc.”. Analytical Chemistry, 49, pp 280A-300A (1977).


Rittenhouse Beats Fraunhofer!

“By pursuing these experiments it is probable that new and interesting discoveries may be made respecting the properties of this wonderful substance, light….but want of leisure obliges me to quit the subject for the present… ” David Rittenhouse in a letter to Francis Hopkinson (1786).

“Want of leisure?” That is certainly understandable! Rittenhouse was the Treasurer of Pennsylvania and had other duties in the newly-formed USA. He would become the first Director of the US Mint in 1792. Hopkinson, a signer of the Declaration of Independence, caused Rittenhouse’s temporary loss of leisure when he sent him the initial letter (March 16, 1785) describing what he saw (diffraction) while looking through a silk handkerchief. But should Rittenhouse have taken the time off from his work on diffraction gratings?

David Rittenhouse

“It is difficult to point to another single device that has brought more
important experimental information to every field of science than the
diffraction grating. The physicist, the astronomer, the chemist, the
biologist, the metallurgist, all use it as a routine tool of unsurpassed
accuracy and precision, as a detector of atomic species to determine the characteristics of heavenly bodies and the presence of atmospheres in the planets, to study the structures of molecules and atoms, and to obtain a thousand and one items of information without which modern science would be greatly handicapped.” (J. Strong, J. Opt. Soc. Am. 50 (1148-1152), quoting G. R. Harrison), from Diffraction Grating Handbook, 5th edition, Christopher Palmer, Thermo RGL.

Big Diffraction Gratings at LLNL
NASA IRIS Telescope with Imaging Spectrograph, with grating, first light July 2013

It’s tough to say who discovered/invented the diffraction grating. Isaac Newton wrote in Opticks about “scratches made in polished plates of glass.” A contemporary of Newton, James Gregory, studied diffraction patterns produced by bird feathers. However, it looks like Rittenhouse in 1785/86 was the first to build and use a diffraction grating to make spectral measurements. Rittenhouse said, “…I made a square of parallel hairs about half an inch each way. And to have them nearly parallel and equidistant, I got a watchmaker to cut a very fine screw on two pieces of small brass wire. In the threads of these screws, 106 of which made one inch, the hairs were laid 50 or 60 in number…” That was one year before Fraunhofer’s birth and three decades before his experiments. But Fraunhofer did not take leisure; he finished the job!

Joseph von Fraunhofer

For an excellent summary of Rittenhouse’s experiments and results, see I. D. Bagbaya, “On the History of the Diffraction Grating,” Soviet Physics Uspekhi Vol. 15 No. 5, p. 660-661, March-April 1973.