The Nineteenth Century 205 



thought to be the most combustible of all known substances, and 

 is widespread in the animal world. Moreover, in burning it pro- 

 duces an acid. 



Placidus Heinrich, whose real name was Joseph Heinrich, was a 

 Benedictine monk at the Royal Monastery of St. Emmeran near 

 Regensburg. With the exception of the years 1791 to 1798 as pro- 

 fessor of natural science, mineralogy and meteorology at the Uni- 

 versity of Ingolstadt, Heinrich spent most of his life at the monas- 

 tery. He was teacher of philosophy and physics at the Lyceum and 

 also head (" Capitular ") of the high cathedral. In addition to his 

 work on luminescence he published in the fields of pyrometry, ther- 

 mometry, and meteorology. 



The introduction to his book tells how he had always been in- 

 terested in the nature and properties of light. In 1776 he began a 

 study of mathematics, physics, and chemistry, noting that the newer 

 knowledge of the latter two subjects would be particularly important 

 for an understanding of the nature of light. He studied Newton's 

 Principia and Priestley's History and Present State of Discoveries 

 Relating to Vision, Light and Colours, reading the book through 

 " more than once." Luminescences intrigued him most of all. He 

 remarked that "it is unbelievable what a well prepared eye can see 

 in the dark . , . quite new phenomena show themselves; complete 

 darkness and a sensitive eye are for us a microscope to discern the 

 smallest atoms of light." 



JEAN PHILIBERT DESSAIGNES 



The winner of the French Institute prize, Jean-Philibert Des- 

 saignes was at that time Director of the school (Pensionat) of 

 Vendome. His essay was published serially in the Journal de 

 Physique, beginning in 1809 under the title " Memoire sur la Phos- 

 phorescence," and was followed by a number of papers in 1810 to 

 1812 dealing with additional aspects of the subject, such as lumines- 

 cence from compression of gases. There are five chapters, the first 

 outlining the field and classifying the various types of luminescences, 

 the second, third, and fourth dealing with phosphorescence by rise 

 of temperature, by insolation, and by collision, respectively, while 

 the fifth was reserved for spontaneous phosphorescence, including 

 luminous wood and fish, because their light was not then known to 

 be biological in origin. 



Dessaignes divided spontaneous luminescences into two kinds: (1) 

 a transient one as when lime is mixed with water and (2) a lasting 

 one such as luminous wood or lish. His experiments and conclusions 



