Latimer Clarke�s Patent Portable Transit Instrument. The provision of portable instruments to measure the Transit of Venus of 1882 shows that observing had been rendered easier than it was for Green and Cook in 1769 with their different and much larger �portable� transit instruments. While stationary transit instruments were much larger for accuracy, the smaller size, redesigned stand and enamelled finish of this telescope, made by Broadhurst, Clarkson & Co of Farringdon Road, London about 1880, illustrates the evolution of a truly portable instrument.