THE CHEAPEST FORM OF LIGHT. 



is a familiar example, tliougli other of the species attain greater size, and 

 ]ierhaps greater intrinsic brilliancy, especially the Fyrojihorus noctihicus 

 I.inn., found in Cuba and elsewhere. Its length is about 87""", width 

 1 1""", and it has, like I\yrophori, three light reservoirs — two in the thorax 

 and one in the abdomen. To ]»rocure this Cuban fire-fly I invoked the 

 aid of the Smithsonian Institution, and through the kindness of Professor 

 Felipe Poey, of Havana, and Sefior Albert Bonzon, of Santiago de Culja 

 in the Island of Cuba, living specimens of the Pyrojihorus noctilucus were 

 received here during the summer of 1889. I have also to acknowledge 

 m}^ obligations to Professor C. V. Riley and to Professor L. A. Howard, 

 to whose knowledge and kind care I am doubly indebted. 



After a preliminary spectral examination in Washington, I found it 

 more convenient to continue the research at the Allegheny Observatory 

 1)}' means of the very special apparatus supplied by the liberality of the 

 late William Thaw, of Pittsburgh, for researches in the lunar heat- 

 spectrum.* Photometric measurements throughout tlie spectrum of the 

 insect's light were also made. 



I have indicated the steps of the investigation, but the exiieriments 

 have been so largely and so intelligently made by Mr. F. W. Very that 

 it is just to consider him as an associate rather than an assistant in the 

 researches. I shall according!}' in what follows not discriminate between 

 what each has contributed. 



Historical Notes. 



We make no attempt to give any bibliography of the subject, and these 

 notes are confined to what seems important in the history of the i)h3'sical 

 side of it. 



Kathnniel Hulme.j — Exper. 6. A dead shining glow-worm was put 

 upon water, contained in a wide-mounted phial, at the temperature of 58. 

 The phial was then sunk in boiling hot water, and as the heat communi- 

 cated itself to the contents of the phial, tiie light of the glow-worm became 

 much more vivid. 



Exper. 7. Another lucid dead glow-worm was put into warm water, 

 at 114, to see if that degree of heat would extinguish the light, but, on 

 tlie contrar}', its glowing projiert}' Avas augmented. All the water was 

 then poured off", 3'et tlie insect continued to shine for some length of 

 time. 



Exper. 8. Two living glow-worms were put into a one-ounce phial, 

 with a glass stopi)le, and though they were perfect!}' dark at the time, 

 yet if tlie phial was briskly rubbed with a silken or linen handkerchief 

 till it became pretty warm, it seldom failed to make them display their 



* Described in the Memoirs of the National Academj', vol. iv, part ii, p. 112. 

 tPhilos. Trans. Roy. Soc, London, vol. xc, pp. 180, 181, 1800. 



