454 



On Macrauchenia patachonica, Ow. 



[Jane 10, 



I. The Fraunhofer line on the solar spectrum, named h by Angstrom, 

 which is due to the absorption of hydrogen, is not visible in the tubes we 

 employ with low battery and Leyden-jar power ; it may be looked upon 

 therefore as an indication of relatively high temperature. As the line in 

 question has been reversed by one of us in the spectrum of the chromo- 

 sphere, it follows that the chromosphere, when cool enough to absorb, is 

 still of a relatively high temperature. 



II. Under certain conditions of temperature and pressure, the very com- 

 plicated spectrum of hydrogen is reduced in our instrument to one line in 

 the green corresponding to F in the solar spectrum. 



III. The equally complicated spectrum of nitrogen is similarly reducible 

 to one bright line in the green, with traces of other more refrangible faint lines. 



IV. From a mixture of the two gases we have obtained a combination of 

 the spectra in question, the relative brilliancy of the two bright green 

 lines varying with the amount of each gas present in the mixture. 



V. By removing the experimental tube a little further away from the 

 slit of the spectroscope, the combined spectra referred to in II. & III. 

 were reduced to the two bright lines. 



VI. By reducing the temperature all spectroscopic evidence of the 

 nitrogen vanished ; and by increasing it, many new nitrogen-lines make 

 their appearance, the hydrogen -line always remaining visible. 



The bearing of these latter observations on those made on the nebulae by 

 Mr. Huggins, Father Secchi, and Lord Bosse is at once obvious. The 

 visibility of a single line of nitrogen has been taken by Mr. Huggins to in- 

 dicate possibly, first, "a form of matter more elementary than nitrogen, 

 and which our analysis has not yet enabled us to detect *, and then, 

 secondly, " a power of extinction existing in cosmical space" "f\ 



Our experiments on the gases themselves show not only that such 

 assumptions are unnecessary, but that spectrum analysis here presents us 

 with a means of largely increasing our knowledge of the physical constitu- 

 tion of these heavenly bodies. 



Already we can gather that the temperature of the nebulas is lower than 

 that of our sun, and that their tenuity is excessive ; it is also a question 

 whether the continuous spectrum observed in some cases may not be due to 

 gaseous compression, 



II. " On the Molar Teeth, lower Jaw, of Macrauchenia patachonica, 

 Ow." By Professor Owen, F.R.S. Received April 21, 1869. 



(Abstract.) 



The intraneural course of the vertebral arteries is limited, in the class 

 Mammalia, to the Ungulate Series, and is present in very few of these. Of 



* Phil. Trans. 1804. p. 444. t Ibid. 1808. p. T>44. 



