82 LIFE AND WORK OF SIR JAGAD1S C. BOSE 



necessary strain in materials less sensitive to light than 

 are silver salts. 



Mechanical pressures may also produce images capable 

 of development, the so-called ' pressure-marks ' ; and, by 

 electric strain, the ' inducto-scripts/ 



At this time (1901) Bose was interested in the question 

 of obtaining photographs without the action of light. 

 Various radio-active substances were being found whose 

 emanations affected the photographic plate. But Bose 

 worked with substances which ordinarily were not radio- 

 active. A section of a dried stem of a tree exhibits con- 

 centric markings, due to unequal growth in different 

 seasons ; these different rings, according to Bose, should 

 emit radio-active particles at different rates under the action 

 of stimulus. He enclosed a section of a stem in a dark 

 box, with a photographic plate in front of it, but not in 

 contact. Outside the box were two metallic plates, which 

 were in connection with a machine which caused rapid 

 electric oscillation in the intervening space. Under the 

 action of this stimulus the radio-activity of the wood was 

 evidenced by an extraordinarily clear impression of its 

 structure given on the photographic plate this, be it 

 remembered, without the intervention of light. The accom- 

 panying reproduction (Fig. 2) is the photograph of a leaf of 

 Bo-tree taken by the above method. By taking similar 

 photographs, he obtained remarkable results with various 

 stones and crystals, which revealed characteristic differences 

 in their composition. A new field of investigation was 

 opened out for immediate exploration ; but all this had 

 to be indefinitely postponed on account of another line 

 inquiry which, as we shall see later, demanded his 

 of undivided attention. 



His theory of molecular strain, however, has been fruitful 

 in physical and chemical researches ; and subsequently 

 found corroboration from Hartley in his work on the 

 absorption spectra of solutions of metallic nitrates. In 

 summarising his results he refers to ' three remarkable 



