260 A BRIEF SURVEY OF HUMAN HISTORY

clinical insight. The following observations by him on small-
pox and measles are interesting :—

The outbreak of small-pox is preceded by continuous fever,
aching in the back, itching in the nose and shivering during sleep.
The main symptoms of its presence are : back-ache with fever,
wincing pain in the whole body, congestion of the face, sometimes
shrinkage, violent redness of the cheeks and eyes, a sense of
picture in the body, creeping of the flesh, pain in the throat and
breast accompanied by difficulty of respiration and coughing, dry-
ncstt of the mouth, thick salivation, hoarseness of the voice, head-
ache and pressure in the head, excitement, anxiety, nausea and
unrest. Excitement, nausea and unrest are more pronounced in
measles than in small-pox, while the aching in the back is more
severe in small-pox than in measles.1

The name of al-Birum (973-1048) is familiar to readers
of early Muslim history in India. He came to India with
Mahmud of Ghazni. But few, perhaps, realise the nature
of his contributions to various branches of knowledge. Fami-
liarly known as *the master' (d-ustadh) he was a physi-
cian, astronomer, mathematician, physicist, geographer and
historian. In physics his greatest achievement is the nearly
exact determination of the specific weight of eighteen pre-
cious stones and metals. But, by far the most important of
Muslim scientists of this age was Abu * Ali al-IJasan ibn al-
Jfaytham (Alhazen) of^ Basra (965 A.D.). Though his
original work in Arabic, On Optics, is lost, it has survived
in Latin translation. In it he opposes the theory of Euclid
,and Ptolemy .that the eye sends out visual rays to the object
of vision. He discusses the propagation of light and colours,
optic illusions and reflection, with experiments for testing
the angles of incidence and reflection. In examining the re-
fraction of light-rays through transparent mediums "he

1. The Legacy of Islam, pp. 323-24.