878 



SCIENCE 



[N. S. Vol. XXVI. No. 677 



tioned telescope is sucli that images of the 

 faintest-known isolated stars can (witli the 

 aid of a powerful magnifying glass) he 

 plainly seen on a photographic plate ex- 

 posed' for less than five minutes in the 

 focus. When this instrument is turned to 

 the sun all known metals are melted and 

 vaporized. A circular hole equal in size 

 to the sun's focal image is almost instantly 

 formed in a thin plate of sheet-iron held in 

 the focus ; by taking a much thicker piece the 

 vaporization of the boiling-iron image of the 

 sun (held in place by capillary action with 

 the bordering plate of cold iron) can be ob- 

 served at leisure until a hole is again formed. 



To obtain a known value of T for a meas- 

 ured value of D the aperture of this mirror 

 was gradually reduced (by means of circular 

 openings, of different diameters, cut in card- 

 boards placed centrally over the mirror) until 

 a strip of platinum plate could just be melted 

 when held in the focal plane. With the sun 

 at 54° zenith distance, in a clear atmosphere, 

 the corresponding diameter was found to be 

 eighteen inches. 



Neglecting for the present the corrections 

 due to aberrations and absorptions in the tele- 

 scope and in the atmosphere, we have the fol- 

 lowing approximate values for substitution in 

 formulas (4), (6) and (Y) : 



i) = 18.0 in. 

 d = 0.337 in. 



f-y = 44000 



T=2000°C. 



The uncorrected results are, therefore. 



Absolute temperature of space ==t^0°.7C. 

 EflFeetive surface temperature of the sun = 



to =30800° C. 



The instrumental corrections (due mostly to 

 absorption at the silver surface of the mirror) 

 increase the value of t from 0°.70 to 0°.Y5. 

 The effect of atmospheric absorption on the 

 intensity of ether vibrations must next be 

 considered. My information on this subject 

 is based upon a long series of photographic 

 observations (on certain iixed stars) which I 

 made, reduced and discussed more than six- 

 teen years ago; the work (8vo, pp. 89) was 



published in 1893 under the title " Terrestrial 

 Atmospheric Absorption of the Photographic- 

 Bays of Light " and forms No. 3 of " Con- 

 tributions from the Lick Observatory." The 

 tabular data on page 86 of this work give, 

 for 54° zenith distance, the intensity (or 

 brightness) 0.61, the brightness at the zenith 

 being unity. J£ the temperature of the sun's 

 focal image varies according to the same law, 

 the value of t is increased from 0°.Y5 to 1°.23 

 in the zenith; this value must, finally, be 

 further increased by a still undetermined cor- 

 rection for absorption in the zenith; if we 

 assume a one-fourth increase in the tempera- 

 ture due to this cause we have iinally 



Absolute temperature of space ^ 1°.5 C. 

 Effective surface temperature of tbe sun 



= 66000" c: 



It should be explicitly stated that the for- 

 mulas are derived for the theoretical case of 

 the earth without an atmosphere, or of observa- 

 tions made in free space. In actual observa- 

 tions T denotes the rise in temperature above 

 the temperature of the surrounding medium 

 and, therefore, is equal to the absolute tem- 

 perature of the sun's focal image minus the 

 absolute temperature of the air at the place 

 of observation. J. M. Schaeberle 



Ann Aebok, 



November 24, 1907 



A NOISELESS ROOM FOR SOUND EXPERIMENTS 



'For many experiments in laboratories of 

 physics, physiology and psychology a place is 

 needed from which all, or nearly all, external 

 sound can be excluded. An absolutely noise- 

 less room opens up numerous new possibili- 

 ties of research, especially in the fields of 

 sound physiology and psychology. For this 

 reason rooms have been constructed in many 

 laboratories, but all the attempts to produce a 

 noiseless room that are known to the writer 

 are more or less unsuccessful, with the excep- 

 tion of the room to be described here. 



The room to which reference is made is in 

 the Physiological Institute of the University 

 of Utrecht, Holland. It has been constructed 

 under the direction and has been used by 

 Professor H. Zwaardemaker, to whom I am in- 



