SECRETS OF THE ANCIENTS

Evening Post, Volume CIX, Issue 51, 1 March 1930, Page 20

SECRETS OF THE ANCIENTS

PHOTOGRAPHING. INVISIBLE WRITING

Palimpsests, or ancient manuscripts in which the original writing lias been erased and the parchment used a second time, are now examined with ultraviolet rays, under which the partially erased original becomes ' visible again and can bo photographed for permanent record, Leonard: .V. Dodds, in an account contrib.utett to "Antiquity" (Gloucester, England), gives the following account of the method, which may, when widely applied, reveal treasures of ancient literature hitherto believed -to be lost.. He writes: —

plate and a deep orange dye is used to make the filter, and this is contained between sheets of uviol blue glass, but in the Hanovia apparatus, one of the most widely used, this" typo of filter has been superseded entirely ty a new glass, almost black, 'which transmits the ultra-violet rays only. •■ • "When examined beneath these rays, various substances, including many dyes, fluoresce.distinctly, and each differing substance exhibits a characteristic colour. When, a substance capable/of fluorescing is excited by filtered ultra-violet, these invisible rays are changed into visible light of longer wave-length, and a curious glow, to which the term fluorescence is applied, is seen. ■ . .■• "When an old manuscript is examined in this way, the tints and dyes left in the parchment from the earlier writings fluoresco distinctly from those of. tho visible text and from the-parch-ment itself, and the palimpsest can easily be distinguished, By using v special filter the later writings may bo eliminated and a photograph, taken of tho earlier script only, but it is of probably greater" interest to see the two texts on one print. The visible, writings' appear as if in outline type— that is white letters with a narrow black edge—and underneath, or often trans verbally, may be seen the dark grey lettering of the original -text. Slight imperfections duo to the varying action of the cleaning process are to be expected, but it is seldom that a-ny difficulties in deciphering occur which are duo to visibility. "It is an extraordinary development of science which thus enables writing erased so long ago to bo read again, and while the ability to photograph the fluorescence, makes a permanent record . ready for ' immediato: reference, testing with.: ultra-violet rays has the great advantage over other . methods using chemicals which might be employed, iii that no damage is caused to the existing writings.; The ' Codex Paulinus.at Wurzburg, which contains the thirteen epistles of St. Paul and the Epistle- to the Hebrews, or tho Codex Ambrosianus,: formerly at Bob" bio,, now at, Milan, may probably yield new matter of much interest." - "

"Owing, to tho labour aud cost of production, parchments used in olden days for writing upon wcro not destroyed when time had rendered a document worthless. ' Instead, they were carefully, cleaned by chemical or mcchaiiical means aud used a second, and oven a third tiin<v 'In many cases the earlier writings would bo of much greater historical ; interest than the superimposed aud visible text if only it wore possible to read them, and tins, strange as ifcniay seeni, can now be done'l By using the method developed from the researches of Professor G. K. Kogel, of Vienna,- writings which were erased hundreds of years^ ago can be read, and photographs taken for permanent, record, and when the method is more widely used a considerable amount, of; material^ will bo available which may be of the'greatest historical importance. ' "Ultra-violet rays are the agent by which these palimpsests are deciphered, : and they? are > generated by. a lamp of-the familiar mercury vapour type. In this instrument a direct current of electricity is , passed through 'tho vapour of niolten mercury contained in a quartz generator,-and electrons in the form of ultra-violet. energy are driven off similarly to X-rays. The burner is' housed in a box-like structure with suitable, arrangements for observation and insertion of the camera lens, and all. rays emitted by the lamp other than the ultra-violet are screened from the ; abject examined by. the provision of a special filter which is. permeable to this group only. Consequently tho manuscript is illuminated by a beam of invisible ultra-violet rays only. In some lamps a solution; of copper-sul-