SCIENTIFIC CONGRESS OF CARLSRUHE. 373 



a lecture, which it would be difficult here to reproduce, on the 'physical 

 causes of harmony and disharmony, audience was accorded to the modest 

 and illustrious Schwerd, whose valuable labors in optics are the fruit 

 of the few hours left him by his professional engagements as a private 

 teacher of literature in his native city of Spire. The subject of his 

 present lecture was a ^photometer constructed by himself, with which 

 he has been enabled to make a series of observations on the fixed and 

 the variable stars. He did not exhibit his apparatus, and the explan- 

 ations given of it are not of a nature to be understood without draw- 

 ings; but according to the testimony of physicists who have seen it, 

 and the judgment of the learned astronomer, Argelander, this photo- 

 meter is calculated to render important service in observatories. 



VIII. 



Calorific Intensity of the Solar Spectrum— Calorific Spectrum— Chemical Spectrum— Lu- 

 minous Spectrum — Index of Refraction of Calorific Rays — Universal Scientific Congress. 



The sitting of the section was closed by M. Muller, professor of 

 physics in the University of Fribourg-en-Brisgau. M. Muller is known 

 to physicists by a series of admirable labors, and especially by his 

 researches on the magnetic maximum of magnetized bars ; he is known 

 to studious youth by a treatise on physics, which he reedits every two 

 years, which at first was only the translation of a French work, but, 

 though still retaining the title of that work, has not the less become 

 an original treatise, entirely independent of that of M. Pouillet. I 

 might appeal for the truth of this to those French professors who read 

 German, and who have — all of them — in their libraries, one or other of 

 the numerous editions of Muller. 



In the lecture of to-day, M. Muller submitted his researches on the 

 calorific intensity of the solar spectrum. By means of the heliostat of 

 M. Silbermann the elder, he directs the solar rays through prisms of 

 different kinds, and determines the calorific intensities by means of the 

 apparatus of Melloni. We know, through this savant, that rock salt 

 is the only diathermanous substance which allows the heat to pass en- 

 tirely, while other bodies always absorb more or less of it. We know, 

 also, that in placing a thermometer in the different tints of the solar 

 spectrum the temperatures irMicated are different ; they augment in 

 proportion as they advance towards the red, and diminish towards the 

 other extremity. The thermoscopic apparatus detects nothingin this 

 respect beyond the violet and outside of the visible spectrum ; it is,on 

 the contrary, sensibly impressed at the opposite extremity, affording 

 an evident proof that the calorific spectrum is not superposed purely 

 and simply on the luminous spectrum. 



As much may be said of the chemical spectrum, which occupies, 

 however, the other extremity of the luminous spectrum. 



