II.1- The first steps: the metallic lens

Father Himalaya, from his early days, saw solar energy as means to provide energy not just for the production of hot water or steam, but as a direct means to provide energy for industrial processes, in particular to those associated with materials production or processing, if high enough temperatures could be achieved. Among other objectives, he wanted to produce nitrogen based agricultural fertilizers by extracting the nitrogen directly from the air! He could never achieve that with his devices, as we can today well understand, but he managed to achieve perhaps the highest controlled temperatures of the day, about 3800°C, in the solar furnace of his pyheliophoro, a truly remarkable achievement.

If not before, at least in Paris, at the end of the turn of century, he became quite likely familiar with the works of A. Mouchot [2], Louis de Royaumont [3], Charles Metelier [4]. Also, mainly from his corresponcence and from documents found among his belongings, it is fair to assume that he must have had some degree of familiarity with the works of John Ericson [1,8] W. Adams [1,8], Calver [1,8,5], Aubrey Eneas [1,6,7,8], among others.

He was critical of the devices produced by Mouchot-Piffre, and soon understood that he needed to modify them in order to obtain higher temperatures and also in order to break the mechanical coupling between the solar furnace ( placed in the "focal zone") from the structure supporting the mirrors. If possible he also wanted a stationary solar furnace, while only the optics would do the necessary tracking of the sun’s apparent motion in the sky.

In Fig1.(a) the device developed by Mouchot-Piffre is shown, a paraboloid like shaped structure with reflecting inner walls, and a furnace place along its optical axis.

(a) (b)

Fig.1.- (a) Solar device of Mouchot-Piffre (b) parabolic trough of Ericson

Truncated cone like shaped mirrors (Eneas Fig.1. (c)[6,7], Pasadena, California, 1901) and large flat ones (Calver, [5]Tucson, 1901) were among some of the solar optics of the day. John Ericson [1,8] proposed a parabolic shaped mirror in 1880 (Fig. 1(b)), but Himalaya’s ideas went in rather different directions.

References [5,6,7] are explicit instances of Portuguese magazines dedicating space, in those days, to those and other inventions and F. Himalaya likely read them. It was not possible to consult the referred magazines and therefore their level of technical detail is not known to the author. However these were publications for a general audience and little should be expected beyond some photos or drawings and a reference to the purpose of the inventions. .

To the interested reader the author recommends the first section of a modern book [8] containing an interesting introductory chapter on the history of solar energy. This book makes an explicit mention of Father Himalaya and his crown solar achievement — the Pyrheliophoro — at the St. Louis Fair of 1904.

He soon understood that the very high concentration factor he needed required two axis type tracking. With materials processing in mind, he needed solutions that would not have, in his own words, "the furnace between the reflector and the sun”. He thus first thought of lenses to do the job, since these could send the concentrated light down and out, towards the target. However the required dielectric (glass!) lenses were not a practical idea in those days and his first remarkable attempt can be seen in Fig.2 and 3. It is a metallic Fresnel lens type, done with flat-strip — mirrors, ring shaped, the whole ingeniously tracking the sun in elevation and compensating for the earth’s rotation, by moving together on circular rails.

Fig2.- Figures from Patent [10]

Fig.3(a)- the device and Himalaya standing in front of it, in Paris

His experiments were carried out in the French Pyrenees, (Castel d’Ultrera) not far from Odeillo and Font-Romeu (of later day fame, for very similar solar reasons!)

The results he obtained were not as good as he expected, but it seems that he was able to achieve temperatures in excess of 1500°C (melting iron), a remarkable achievement, given the choice he had of materials for the mirrors, and a good measure of the mechanical precision with which he was able to produce his device. It should be noted that the solar furnace itself was object of careful developments, to be able to contain the materials he was melting/processing with it. His temperature measurements were crucially dependent on what he was able to melt.

In fact the furnace itself was the object of patents, perhaps the most important of which being Patent [9].

Fig.4 is taken from that patent, showing a radiative type furnace, where the side walls c, c’ were to be heated with the burning of fuel and the heat radiated into the triangular shaped cavity was to be concentrated (focussed) down onto the hot cavity F, by a paraboloid shaped upper wall d. This furnace was later very easily (and much better) adapted to the solar focussing optics to be described next, with solar radiation coming trough an aperture placed in d and the side walls c, c’ now serving as a second stage concentrator.

In the process of these developments he invented also a radiometer — to measure solar radiation intensity using his metallic lens concept.