Agriculture on a large scale:

Crops had  to  be  planted and  harvested in  the  right season. Floods were a recurrent phenomenon  in the river valleys, for which it was essential to be prepared beforehand. The observation of sun and stars  to  fix the length of a year became so  precise  that  already  in 2700 B.C., the Egyptians were able  to  fix  it at 365.2422 days! Sumerians  and their successors  in Mesopotamia adjusted t'he solar (sun-based)  and lunar (moon-based) calendars through accurate observations.  They invented the sexagesimal system of 360 degrees in a circle (near enough to the days in  a year), 60 minutes in  an hour, 60 seconds in a minute.  The exercises were carried out using mathematical tables and ied to algebra and arithmetic of  the later epochs. Another occupation  that came to be very prestigious with  the growth of  cities was that of medicine.  Although the practice of medicine was limited to treating wounds, dislocations, fractures etc., the practitioners could successfully diagnose many diseases. They could compare cases with one another, notice different diseases and record them.  From such descriptions, orally passed on  to later generations, arose the sciences of  anatomy and physiology.  Practitioners  of medicine also had  the knowledge of plants and mineral substances to prepare drugs for various diseases. They grew plants and herbs for this purpose.  It is from this source  that the science of botany arose later. The basis for chemistry was laid in the observations  and practices of jewellers, metal- workers and potters.  They knew about at least nine chemical elements-gold,  silver, copper, tin, lead, mercury, iron, sulphur and carbon, and also about a variety of dry and liquid reagents.  The process of  smelting ores, of purifying metals, of colouring  them, of adding enamel%-all  involve complex chemical reactions  that were learnt by many trials and experiments. However, chemistry never rose to the rank of a recognised science  in  the 'Bronze Age.