HERMAN LTJDWIG FERDINAND HELMHOLTZ was born at Pottsdam, August 

 31, 1821. He was first military physician, and afterwards assistant of the 

 Astronomical Museum in Berlin (1848), and subsequently Professor Extra- 

 ordinary of Physiology at the University of Konigsberg (1849 to 1852). He 

 became Professor of Physiology at the University of Bonn in 1855, and in 

 1858 accepted the physiological chair in the University of Heidelberg. The 

 lecture which follows was delivered at Konigsberg hi 1854. He is an emi- 

 nent investigator, and an able promoter of the recent philosophy of forces ; 

 but of his life we have fewer particulars than of his accomplished translator. 



The ancestors of JOHN TYNDALL emigrated from England to the eastern 

 or Saxon border of Ireland about the middle of the last century. He was 

 born at the village of Leighlin Bridge in 1820, where he received his early 

 education and acquired a taste for mathematics. In 1839 he left school 

 and joined the Ordnance Survey as a civil assistant, where he became in 

 turn draughtsman, computer, surveyor, and trigometrical observer. He was 

 five years connected with the survey, and for three years occupied as rail- 

 road engineer. In 1847 he became teacher in Queenswood College in Hamp- 

 shire, a school for agriculturists and engineers, where he was distinguished 

 for his mild but efficient discipline. Professor Frankland, the chemist, was 

 here joined with him hi the work of instruction, and in 1848 the two friends 

 left the institution and went to the University of Marburg in Hesse Cassel, 

 to study with the eminent chemist, Bunsen. In 1851 Professor Tyndall 

 went to Berlin and worked at the subject of diamagnetism in the laboratory 

 of Professor Magnus. He returned to London the same year, and was 

 elected Fellow of the Eoyal Society in 1852. 



Through the influence of Dr. Bence Jones, General Sabine, and Professor 

 Faraday, he was appointed Professor of Natural Philosophy in the Royal 

 Institution in 1853, an appointment which he now holds. In company with 

 his friend, Professor Huxley, he visited the Alps hi 1856 ; and returning each 

 succeeding year, he accumulated the observations and adventures which are 

 so graphically described in his "Glaciers of the Alps," published in 1860. 

 Professor Tyndall has worked with eminent success at various scientific 

 questions, but he is chiefly distinguished for his original and elaborate re- 

 searches on the relations of radiant heat to gaseous and vaporous matter. 

 These researches are given hi his able work on " Heat as a mode of Motion," 

 issued hi 1863. As an experimenter, Professor Tyndall is marked for his 

 caution, accuracy, and tireless perseverance under difficulties ; as a writer, 

 for his clear, vivid, and vigorous style. 



