On 25 August 1965 spectrograms centered on the line BaII 5854 were obtained with the McMath Solar Telescope of Kitt Peak National Observatory under conditions of very good seeing so that the granulation velocity field was clearly revealed. These spectrograms were obtained at the centre of the disk in the fifth order of the grating, yielding a dispersion of 9.73 mm/,~. Using a slit width of 100 microns, the exposure time was 0.5 sec on Linagraph Shellburst film developed 8 min in HC 110.
Isophotal maps have been obtained using the scanning isophotometer of the McMath-Hulbert Observatory of the University of Michigan. A section of the spectrogram exhibiting the most fine-scale detail and the corresponding isophotal map are reproduced in Figure 1. The scale of the isophotal map is enlarged in the direction of the dispersion 2.54 times its scale in the direction of the slit. The scanning aperture was 0'.'25 high and 15 mโข wide. From contours corresponding to about 30 mA either side of the mean centre of the spectral line the rms velocity was found to be 0.37 km/sec, corresponding to a random turbulent velocity of 0.52 km/sec.
Along one isophote, at an average distance of about 60 mA redward from the line centre, there are several sharp displacements whose widths are 0'.'8 to 176. These sharp redward displacements are seen to coincide with the dark streaks in the continuum and so must represent the intergranular lanes. If the magnitude of these displacements is taken as the displacement of the mean of corresponding blue and red isophotes (measurement A in Figure 2), a maximum velocity of 2.2 km/sec is obtained. So far as we are aware, this is the highest granular velocity ever determined from a solar spectrogram in a photospheric line. Note that if the displacement of the red isophote alone is determined (measurement B in Figure 2), velocities of over 3 km/sec can be obtained, but these values are misleading because of the unknown effects of the continuum-brightness fluctuations.
The corresponding 60 m~ isophote in the blue wing of the line does not display such sharp displacements, nor, in general, do any of the isophotes in the blue wing display such strong structure as the corresponding isophote in the red wing. The isophotal map confirms the visual impression one receives from spectrograms obtained under conditions of very good seeing: Lines have gentle scallops on the blue side and sharply pointed cusps on the red side. This implies that material falls rapidly in the very narrow intergranular spaces. Also, it is obvious from the isophotal map * Kitt Peak National Observatory Contribution No. 307. ** Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation.