World first encyclopaedia (Ikhwan us Safa) was invented / prepared by 9th Fatimi Imam Molana Ahmed al-Mastoor a.s. The count (adad) of word "Ahmed" is 53, this encyclopaedia has 52 epistle and one collective risala totalling 53. Prophet Mohammad pbuh taught the grade first and left the teaching of next level (grade second) course with Mola Ali a.s. and announced "Ana madinatul ilm wa Aliyun baboha" (I'm the city of knowledge and Ali is its entrance gate, enter in the city from its entrance gate.) i.e. those who want to pursue the higher level education they may enrol with Mola Ali a.s. After the death of Prophet pbuh the flow of knowledge (Allah's messages) to commoners got stopped because the authorised nominee of Allah was pushed out from the office of caliphate. To quench the thirst of education seekers the then rulers of Abbasid took refuge at Greek and Indian philosophical literature, they were translated in Arabic and Islam was looked from the spectacles of non-Islamic (Greek & Indian) philosophy. The students / scholars elite got drowned in the corrupt Greek / Indian philosophies. In such dark times the correct Islamic status of every faculty of knowledge was revealed by Allah via his nominated authorised servant 9th Fatimi Imam Molana Ahmed al-Mastoor a.s. and thus took the invention of world first encyclopaedia: Ikhwan us Safa.
 Measuring time - Fatimid regime invented the idea of measuring the time by clock - the world first pendulum was invented by Fatimid. World first Sundial clock was invented by Fatimid.
 Algebra or Universal Arithmetic the method of calculating, in-determinative quantities, or investigating the relations that subsist among quantities of all kinds, whether arithmetical, or geometrical was developed from the form that Diophantus had left. Fatimid regime also gave to trigonometry its modern form substituting signs for chords, which had been previously used; they elevated it into a separate science. In Astronomy Fatimid regime not only made catalogues but maps of the stars visible in their skies, giving to those of the larger magnitudes the Arabic names which they still bear on our celestial globes. Fatimid ascertained -
The size of the earth by the measurement of a degree on her surface,
Determined the obliquity of the ecliptic,
Published corrected tables of the sun and the moon, fixed the length of the year,
Verified the precision of the equinoxes.
 Chemistry - Fatimid regime discovered the most important re-agents:
Sulphuric acid and
 Medicine - Fatimid regime was first in the whole world to publish pharmacopoeias or dispensatorias, and to include in them mineral preparations.
 Mechanics - Fatimid determined the laws of falling bodies, had ideas, by no means indistinct, of the nature of gravity; they were familiar with theories of the mechanical powers.
Hydrostatics - Fatimid constructed the first table of the specific gravities of bodies, and wrote treatise on the floatation and sinking of bodies in water.
Optics - Fatimid corrected the Greek misconception (which was blindly adopted by Abbasid regime), that a ray proceeds from the eye and touches the object seen, introducing first time to the world the hypothesis that the ray passes from the object to the eye. They understood the phenomena of reflection and refraction of light. Mumineen of Fatimi Dawat Alhazen made the great discovery of the curvilinear path of ray of light through the atmosphere, and proved that we see the sun and moon before they have risen, and after they have set.
 The then world biggest library was that of Fatimi Imams. And it remained the biggest for following 1,000 (one thousand) years.
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