Between five and six o’clock on the afternoon of the 18th of May, while I was absorbed in my writing, I was suddenly startled by the outcry of a number of my people calling me to make haste out and witness the singular appearance which was arresting their attention on the south-west horizon. Great masses of clouds were covering the declining sun, whilst all below the heavy cumulus the heavens gleamed with the golden shimmer of a glorious sunset. Like a pile from the mighty Alps, stern and imposing, surrounded by dazzling glaciers and by many an avalanche, the central clouds of this great gathering massed themselves in ponderous layers which rolled majestically to the north. Starting out abruptly from the brilliant glare of the setting sun, these layers on their upper edge distinctly assumed the form of three vast swellings, while around the margin of each of these there gleamed the light of an unearthly glory; colours of the richest hue combined to give an effect as though each of the projecting accumulations were circled by a rainbow. Midway between the vanishing violet of the bow and the sombre ridge of cloud streamed a flood of light which repeated itself upon the superior margin of the wondrous spectrum. In three directions (issuing not directly as from the sun in the centre of the mass, but as though two parhelia besides contributed their power) there rose separately from each of the three tumescent rolls of cloud shadowy beams of light embracing the whole firmament above, whilst in addition to all this, there were secondary groups of beams diverging from the angles where the rainbow arches intersected. An appearance somewhat similar to these shadowed rays or streaks of alternate light and shade, resulting from the unequal masses of the floating clouds, has been recorded by Professor Tyndall as witnessed in Algiers. The colour of the rainbows on their edge nearest to the sun, and in consequence approximate to the clouds, was so remarkable that it could not fail to excite my attention. Altogether it was a spectacle not to be forgotten. The rainbow-like phenomenon had not the appearance of being an ordinary arch repeated thrice, but was one scallopped bow composed of three distinct but successive limbs: it continued for about five minutes, and allowed me ample time to make a sketch of its striking features.[36] During September I found an opportunity to make a third excursion to the Tondy, and had the good fortune to make some valuable additions to my botanical store, but apart from this my days glided on without variety, and I have no episodes of interest to relate.